RESSALVA 

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UNIVERSIDADE ESTADUAL PAULISTA “JÚLIO DE MESQUITA FILHO” 

FACULDADE DE ENGENHARIA 

CÂMPUS DE ILHA SOLTEIRA 

MARCELO BORTOLETTO 

IMPEDANCE SPECTROSCOPY TO STUDY THE HYDRATION PROCESSES OF 

PORTLAND CEMENT WITH AGRICULTURAL WASTES 

Ilha Solteira 

2024



Campus de Ilha Solteira  
 

 

PROGRAMA DE PÓS-GRADUAÇÃO EM CIÊNCIA DOS MATERIAIS 

 

 

 

 

 

MARCELO BORTOLETTO 

 

 

 

 

 
IMPEDANCE SPECTROSCOPY TO STUDY THE HYDRATION PROCESSES OF 

PORTLAND CEMENT WITH AGRICULTURAL WASTES 

 
 

 

 

 

 

A thesis submitted to the Faculdade de Engenharia 

– Campus de Ilha Solteira/UNESP, for the degree 

of Doctor in Materials Science. 

Area of knowledge: Materials Science and 

Engineering. 

 

 

Prof. Dr. Mauro Mitsuuchi Tashima 

Supervisor 

 

Prof. Dr. Alex Otávio Sanches 

Co-Supervisor  

 

 

 

 

 

 

 

 

 

 

 

 

 

Ilha Solteira 

2024



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



 

 

IMPACTO POTENCIAL DESTA PESQUISA 

 

A pesquisa focou no estudo dos processos de hidratação de pastas de cimento Portland 

misturadas com cinzas de resíduos agrícolas. A pesquisa proporciona contribuições 

significativas para o entendimento dos processos de hidratação in-situ do cimento Portland, 

bem como a inflûencia das cinzas de resíduos agrícolas nas reações de hidratação utilizando 

curvas de condutividade elétrica obtida a partir da espectroscopia de impedância. Além disso, 

a pesquisa buscou agregar valor tecnológico aos resíduos agrícolas e contribuir para a mitigação 

dos problemas ambientais relacionados à produção do cimento Portand e descarte destes 

resíduos, visando a utilização de um material mais sustentável na indústria da construção civil. 

 

 

POTENTIAL IMPACT OF THIS RESEARCH         

 

The research focused on the study of the hydration processes of Portland cement pastes 

and blended Portland cement pastes with agricultural wastes ashes. The research provides 

significant contributions to the understanding of the in-situ hydration processes of Portland 

cement, as well as the influence of agricultural wastes ashes on hydration reactions using 

electrical conductivity curves obtained from the impedance spectroscopy. Furthermore, the 

research sought to aggregate technological value to agricultural wastes and contribute to the 

mitigation of environmental problems related to the production of Portand cement and disposal 

of this wastes, aiming to use a more sustainable material in the construction industry. 

 

 



 

 

 
 



 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I dedicate this thesis primarily to 

God, and to my parents, 

Gilvandete and Vladimir (in 

memoriam). 

 



 

 

ACKNOWLEDGMENTS 

I would like to thank my mother Gilvandete, my dear father Vladimir (in memoriam) 

and my entire family for their support and love. 

I would like to especially thank my supervisor and friend Prof. Dr. Mauro Tashima for 

all the shared knowledge and opportunity to carry out this work. 

I would like to especially thank my co-supervisor and friend Prof. Dr. Alex Otávio 

Sanches for all the shared knowledge during this period. 

I would like to thank professors Jorge Akasaki, José Malmonge, Jordi Payá, Lourdes 

Soriano and Maria Victoria Borrachero for their support in the stages of the work. 

I would like to especially thank my great friend Rodrigo Garozi for his friendship, 

advice and all his support in difficult and fun moments in my life. 

I would like to especially thank my great friend Josiane for all her support, friendship 

and advice. 

I would like to thank my postgraduate friends Denise, Gean, Guilherme, Fernando for 

the fun and professional moments, and my friend from Ilha Solteira Mike. I would also like to 

thank all my friends from the MAC group and all the professors and collaborators from the 

Department of Physics and Chemistry and Civil Engineering at UNESP. 

I would like to thank technicians Gilson, Flávio, Ozias and Natália from the Civil 

Engineering laboratory and technician Elton from the Physics and Chemistry department for 

their help with the tests carried out in the research. 

I would like to thank Prof. Dr. Wendel Cleber Soares for the encouragement to pursue 

an academic career, since graduation. 

I would like to thank to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior 

- Brazil (CAPES) - Finance Code 001 and to Fundaçao de Amparo à Pesquisa do Estado de São 

Paulo - FAPESP (Project 2020/16325-0 and CEPID - CDMF 2013/07296-2) for the financial 

support and scholarship. Furthermore, I would like to thank to Universidade Virtual do Estado 

de São Paulo - UNIVESP for the scholarship. 

Finally, thanks to everyone who contributed directly or indirectly to this thesis. 

 
 
 
 
 
 
 
 



 

 

RESUMO 

 

O uso de cinzas de resíduos agrícolas, como a cinza da casca de arroz (CCA), cinza da folha de 

bambu (CFB) e a cinza do bagaço da cana-de-açúcar (CBC) como substitutos parciais do 

cimento Portland contribui para a mitigação dos problemas ambientais associados à produção 

do  cimento Portland. A inserção destes resíduos ocasiona em diversos efeitos na hidratação do 

cimento Portland e modifica as propriedades no estado fresco e endurecido, tornando o 

entendimento das reações de hidratação ainda mais complexos. Nos últimos anos, a 

espectroscopia de impedância (EI) tem se mostrado uma poderosa técnica não destrutiva para 

compreender as reações de hidratação in situ do cimento Portland. Neste sentido, o objetivo 

deste estudo foi compreender os diferentes processos físico-químicos envolvidos na hidratação 

de pastas de cimento e pastas de cimento misturadas com cinzas de resíduos agrícolas (CCA, 

CFB e CBC) por meio de curvas de condutividade elétrica obtidas a partir da técnica de EI. 

Foram avaliadas três porcentagens de CCA, CFB and CBC (0, 10 e 25%, em massa) em 

substituição ao cimento Portland. As medidas de EI foram realizadas em pastas com relação 

água/ligante fixa de 0.40 até 28 dias de cura. Medidas de termogravimetria (TG), difração de 

raios-X (DRX), temperatura em escala temporal, microscopia eletrônica de varredura (MEV), 

dureza Vicat e resistência à compressão foram utilizadas para auxiliar os dados de EI. De acordo 

com os resultados, com base nas inflexões de sua derivada, a curva de condutividade elétrica 

da pasta de cimento foi subdividida em oito regiões diferentes. Uma nova região no período de 

aceleração (região IV) foi identificada, caracterizada pela retomada das reações de dissolução 

e formação de microestrutura, com a pasta em estado semifluido. Além disso, um shoulder 

observado na região VI foi atribuído à formação de fases AFt e reações secundárias de liberação 

iônica na rede de poros. Nas pastas de cimento misturadas, o efeito de diluição, a absorção de 

água pela estrutura porosa das cinzas de resíduos agrícolas e a adsorção de íons em suas 

superfícies foram os efeitos dominantes nas primeiras idades, o que ocasionou na menor 

liberação iônica na solução e um atraso nas reações de hidratação. As pastas de cimento 

misturadas com CBC apresentaram a maior extensão do período de indução e tempo de pega, 

associado ao efeito de diluição e maior teor de perda ao fogo e tamanho de partícula da CBC. 

Por fim, a EI demonstrou ser uma técnica promissora no estudo dos processos de hidratação in 

situ e evolução da microestrutura  de pastas de cimento misturadas com resíduos agrícolas.  

 

Palavras-chave: Espectroscopia de impedância, propriedades elétricas, hidratação do cimento 

Portland, material cimentício suplementar, resíduo. 



 

 

ABSTRACT 

 

The use of agricultural wastes ashes, such as rice husk ash (RHA), bamboo leaf ash (BLA) and 

sugarcane bagasse ash (SCBA) as partial replacements for Portland cement contributes to the 

mitigation of environmental problems associated with the production of Portland cement. The 

insertion of these wastes causes several effects on Portland cement hydration and modifies the 

properties in the fresh and hardened state, making the understanding of hydration reactions even 

more complex. In the last years, impedance spectroscopy (IS) has proven to be a powerful non-

destructive technique for understanding the in-situ hydration reactions of Portland cement. In 

this sense, the objective of this study was to understand the different physical-chemical 

processes involved in the hydration of cement pastes and blended cement pastes with 

agricultural wastes ashes (RHA, BLA and SCBA) through electrical conductivity curves 

obtained from EI. Three percentages of RHA, BLA and SCBA (0, 10 and 25%, by mass) were 

evaluated as replacement for Portland cement. The EI measurements were performed on pastes 

with a fixed water/binder ratio of 0.40 up to 28 curing days. Measurements of thermogravimetry 

(TG), X-ray diffraction (XRD), time scale temperature, scanning electron microscopy (SEM), 

Vicat hardness and compressive strength were used to support the IS data. According to the 

results, based on the inflections of the derivative, the electrical conductivity curve of the cement 

paste was subdivided into eight different regions. A new region in the acceleration period 

(region IV) was identified, characterized by the resumption of dissolution reactions and 

microstructure formation with the paste in a semi-fluid state. Furthermore, a shoulder observed 

in region VI was attributed to the formation of AFt phases and secondary ionic release reactions 

in the pore network. In the blended cement pastes, the dilution effect, water absorption by the 

porous structure of agricultural waste ash and ion adsorption on their surfaces were the 

dominant effects in the early ages, which resulted in lower ionic release into the solution and a 

delay in hydration reactions. SCBA blended cement pastes showed a higher extension of the 

induction period and setting time, associated with the dilution effect and the higher loss on 

ignition content and particle size of SCBA. Finally, IS demonstrated to be a sensitive and 

promising technique to study in situ hydration processes and evolution of the microstructure of 

blended cement pastes with agricultural wastes. 

 

Keywords: Impedance spectroscopy, electrical properties, Portland cement hydration, 

supplementary cementitious material, waste. 

 



 

 

FIGURES LIST  

 

Figure 1.1 - Structure of the research. ...................................................................................... 20 

 

Figure 2.1 - Portland cement manufacturing process (Mikulčić et al. [2]). ............................. 23 

Figure 2.2 - Indicative proportions of minerals during conversion of raw meal into clinker 

(Del Strother [3]). ..................................................................................................................... 24 

Figure 2.3 - Different periods of alite hydration following the Ca2+ concentration evolution 

and the associated heat release (Gartner et al. [10] and Marchon and Flatt [11]). ................... 28 

Figure 2.4 - Schematic representation of the dissolution rate of alite as a function of the 

undersaturation.  Zone II represents the dissolution controlled by etch pit formation and Zone 

I represents the dissolution controlled by step retreat (Juilland et al. [18]).............................. 30 

Figure 2.5 - Representation of the relationship between the maximum of the heat release and 

the growth mode of C-S-H (Bazzoni [12]). .............................................................................. 31 

Figure 2.6 - Typical heat release curve of C3A hydration (Joseph et al. [24]). ........................ 33 

Figure 2.7 - Schematic representation of heat release and the different periods during 

hydration of ordinary Portland cement (Marchon and Flatt [11]). I - dissolution period, II - 

induction period, III - acceleration period, IV - deceleration period, V - continuous slow 

hydration period. ....................................................................................................................... 35 

Figure 2.8 - Global CO2 emissions from the cement industry over the years (Global Carbon 

Project [35]). *Mt = millions of tons. ....................................................................................... 37 

Figure 2.9 - Use of pozzolans derived from agricultural wastes in cementitious materials as an 

alternative to mitigate CO2 emissions in the production of Portland cement. .......................... 38 

Figure 2.10 - Schematic drawing of the effects of agricultural waste ash on the hydration 

process of Portland cement (a) filler effect; (b) nucleation effect; (c) dilution effect and (d) 

chemical effect. ......................................................................................................................... 40 

Figure 2.11 - Theory of impedance spectroscopy (a) AC voltage and current, (b) samples 

under AC simulation and (c) complex impedance plane (Adapted from Zhang et al. [78]). ... 46 

Figure 2.12 - (a) The theoretical Nyquist plot from impedance spectroscopy data of a cement-

based material [96] and (b) Typical Nyquist plot measurement from impedance spectroscopy 

data of a cement-based material. The parameters RS represent the bulk resistance in series, Rint 

is the solid-liquid interface resistance and Rb is the bulk resistance of the sample. ................. 48 

Figure 2.13 - Schematic diagram of Nyquist plot of a cement-based material (Adapted from 

Kim, Suryanto and McCarter [106]. ......................................................................................... 49 

Figure 2.14 - Electrical conductivity/resistivity curves of cementitious materials obtained by 

different authors (a) Schwarz et al. [108]; (b) McCarter et al. [110]; (c) Sanish et al. [107]; (d) 

Taha et al. [85]; (e) Suryanto et al. [86] e (f) Adapted from Huang et al. [84]. ....................... 53 

 

Figure 3.1 - Particle size distribution of anhydrous cement (CPV).......................................... 65 

Figure 3.2 - Flowchart of the experimental program carried out in this study. ........................ 66 

Figure 3.3 - The Nyquist plots of Portland cement paste at different hydration periods. ........ 71 

Figure 3.4 - Conductivity as a function of frequency range of Portland cement paste at 

different hydration periods. Red circles indicate the cusp-point frequency. ............................ 71 



 

 

Figure 3.5 - (a) Conductivity, σ (100 kHz), and its derivative (dσ/dt) as a function of time for 

cement paste (CPV); and (b) Internal temperature of cement paste. ........................................ 73 

Figure 3.6 - Region I at 10 min of hydration (a) Conductivity (σ), derivative (dσ/dt) and 

internal temperature of cement paste in function of log t; (b) XRD diffractogram (A: Alite, 

C3S; AL: Tricalcium aluminate, C3A; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; 

G: Calcium sulfate dihydrate, CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2); (c) DTG curve 

and (d) SEM image. .................................................................................................................. 75 

Figure 3.7 - Region II at 37 min of hydration (a) Conductivity (σ), derivative (dσ/dt) and 

internal temperature of cement paste in function of log t; (b) XRD diffractogram (A: Alite, 

C3S; AL: Tricalcium aluminate, C3A; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; 

G: Calcium sulfate dihydrate, CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2); (c) DTG curve 

and (d) SEM image. .................................................................................................................. 76 

Figure 3.8 - Region III at 49 min of hydration (a) Conductivity (σ), derivative (dσ/dt) and 

internal temperature of cement paste in function of log t; (b) XRD diffractogram (A: Alite, 

C3S; AL: Tricalcium aluminate, C3A; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; 

G: Calcium sulfate dihydrate, CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2); (c) DTG curve 

and (d) SEM image. .................................................................................................................. 78 

Figure 3.9 - Region IV at 88 min of hydration (a) Conductivity (σ), derivative (dσ/dt) and 

internal temperature of cement paste in function of log t; (b) XRD diffractogram (A: Alite, 

C3S; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; G: Calcium sulfate dihydrate, 

CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2); (c) DTG curve and (d) SEM image. ........... 80 

Figure 3.10 - Region V at 240 min of hydration (a) Conductivity (σ), derivative (dσ/dt) and 

internal temperature of cement paste in function of log t; (b) XRD diffractogram (A: Alite, 

C3S; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; G: Calcium sulfate dihydrate, 

CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2); (c) DTG curve and (d) SEM image. ........... 82 

Figure 3.11 - Region VI at 440 min of hydration (a) Conductivity (σ), derivative (dσ/dt) and 

internal temperature of cement paste in function of log t; (b) XRD diffractogram (A: Alite, 

C3S; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; G: Calcium sulfate dihydrate, 

CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2); (c) DTG curve and (d) SEM image. ........... 83 

Figure 3.12 - Region VII at 1 day of hydration (a) Conductivity (σ), derivative (dσ/dt) and 

internal temperature of cement paste in function of log t; (b) XRD diffractogram (A: Alite, 

C3S; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; P: Calcium hydroxide; Ca(OH)2); 

(c) DTG curve and (d) SEM image. ......................................................................................... 85 

Figure 3.13 - Region VIII at 3, 7, and 28 days of hydration (a) Conductivity (σ), derivative 

(dσ/dt) and internal temperature of cement paste in function of log t; (b) XRD diffractogram 

(A: Alite, C3S; B: Belite, C2S; C: Calcite, CaCO3; E: Ettringite, AFt; Monosulfate, AFm; P: 

Calcium hydroxide; Ca(OH)2); (c) DTG curve and (d) SEM image. ....................................... 86 

Figure 3.14 - (a) Evolution of amount of portlandite as a function of time; (b) correlation of 

the amount of portlandite with the electrical conductivity; (c) bound water content as a 

function of time and (d) correlation of the bound water content with the electrical 

conductivity. The electrical conductivity curve is presented to visualize the hydration regions 

in which the hydrates were quantified. ..................................................................................... 87 

 

Figure 4.1 - Particle size distribution of cement and RHA. ..................................................... 95 



 

 

Figure 4.2 - Experimental setup for IS measurements. ............................................................ 96 

Figure 4.3 - (a) Electrical conductivity and (b) derivative (dσ/dt) as a function of time for 

cement, RHA/10 and RHA/25 pastes. .................................................................................... 101 

Figure 4.4 - Electrical conductivity and derivative (dσ/dt) as a function of time for cement (a), 

RHA/10 (c) and RHA/25 pastes (e) and internal temperature of cement (b), RHA/10 (d) and 

RHA/25 pastes (f). The letters A-G indicate the different characteristic hydration points on the 

dσ/dt curve. ............................................................................................................................. 102 

Figure 4.5 - (a) Conductivity (σ) and (b) derivative (dσ/dt) of cement, RHA/10 and RHA/25 

pastes from regions I and II as a function of log t; (c) XRD diffractogram  (A: Alite, C3S; AL: 

Tricalcium aluminate, C3A; B: Belite, C2S; C: Calcite, CaCO3; Ct: Cristobalite, SiO2; E: 

Ettringite, AFt; G: Calcium sulfate dihydrate, CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2) 

and (d) DTG curve of cement, RHA/10 and RHA/25 pastes of point A. The rectangles 

indicated in (a) and (b) represent the extension of the hydration regions of the pastes under 

analysis. .................................................................................................................................. 105 

Figure 4.6 - Electrical conductivity of different RHA/water solutions in function of time 

obtained from the use of a conductivity meter. ...................................................................... 106 

Figure 4.7 - Conductivity (σ) and (b) derivative (dσ/dt) of cement, RHA/10 and RHA/25 

pastes from region III as a function of log t; (c) XRD diffractogram (A: Alite, C3S; AL: 

Tricalcium aluminate, C3A; B: Belite, C2S; C: Calcite, CaCO3; Ct: Cristobalite, SiO2; E: 

Ettringite, AFt; G: Calcium sulfate dihydrate, CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2) 

and (d) DTG curve of cement, RHA/10 and RHA/25 pastes of point B. The rectangles 

indicated in (a) and (b) represent the extension of the hydration regions of the pastes under 

analysis. .................................................................................................................................. 107 

Figure 4.8 - (a) Conductivity (σ) and (b) derivative (dσ/dt) of cement, RHA/10 and RHA/25 

pastes from regions IV e V as a function of log t; (c) XRD diffractogram (A: Alite, C3S; 

AL:Tricalcium aluminate, C3A; B: Belite, C2S; C: Calcite, CaCO3; Ct: Cristobalite, SiO2; E: 

Ettringite, AFt; G: Calcium sulfate dihydrate, CaSO4‧2H2O; P: Calcium hydroxide; 

Ca(OH)2); (d) DTG curve and SEM images (e) cement paste, (f) RHA/10 paste and (g) 

RHA/25 paste of point C. The rectangles indicated in (a) and (b) represent the extension of the 

hydration regions of the pastes under analysis. ...................................................................... 110 

Figure 4.9 - (a) Conductivity (σ) and (b) derivative (dσ/dt) of cement, RHA/10 and RHA/25 

pastes from regions VI e VII as a function of log t; (c) XRD diffractogram (A: Alite, C3S; B: 

Belite, C2S; C: Calcite, CaCO3; Ct: Cristobalite, SiO2; E: Ettringite, AFt; G: Calcium sulfate 

dihydrate, CaSO4‧2H2O; P: Calcium hydroxide; Ca(OH)2); (d) DTG curve and SEM images 

(e) cement paste, (f) RHA/10 paste and  (g) RHA/25 paste of point D. The rectangles 

indicated in (a) and (b) represent the extension of the hydration regions of the pastes under 

analysis. .................................................................................................................................. 113 

Figure 4.10 - (a) Conductivity (σ) and (b) derivative (dσ/dt) of cement, RHA/10 and RHA/25 

pastes from region VIII as a function of log t; (c) XRD diffractogram (A: Alite, C3S; B: 

Belite, C2S; C: Calcite, CaCO3; Ct: Cristobalite, SiO2; E: Ettringite, AFt; M: Monosulfate, 

AFm; P: Calcium hydroxide; Ca(OH)2); (d) DTG curve and SEM images (e) cement paste, (f) 

RHA/10 paste and  (g) RHA/25 paste of point G. The rectangles indicated in (a) and (b) 

represent the extension of the hydration regions of the pastes under analysis. ...................... 115 



 

 

Figure 4.11 - BSE images and EDS mapping of Al, Ca, Si, and S of (a)-(b) cement paste and 

(c)-(d) RHA/25 paste after 28 curing days. ............................................................................ 116 

Figure 4.12 - Compressive strength of cement, RHA/10 and RHA/25 pastes. Different letters 

(a1, a2, and a3) represent significant differences between the RHA blended cement pastes and 

cement paste considering a significance level of 5%. ............................................................ 117 

 

Figure 5.1 - Particle size distribution of Portland cement, BLA, and SCBA. ........................ 129 

Figure 5.2 - Morphological structure of BLA and SCBA. ..................................................... 130 

Figure 5.3 - XRD pattern of Portland cement, BLA and SCBA (A: Alite, C3S; AL: Tricalcium 

aluminate, C3A; B: Belite, C2S; Br: Brownmillerite, C4AF; C: Calcite, CaCO3; H: Calcium 

sulfate hemihydrate, CaSO4‧0.5H2O; P: Portlandite, Ca(OH)2 and Q: Quartz, SiO2). The 

magnified regions in the figure represent the amorphous phase of BLA and SCBA. ............ 130 

Figure 5.4 - Loss of electrical conductivity, Lc (%), for Ca(OH)2:BLA and Ca(OH)2:SCBA 

suspensions tested at: 40 °C; 50 °C, and 60 °C. ..................................................................... 131 

Figure 5.5 - Electrical conductivity of the ash/water solutions in function of time. The 

ash/water ratio used was 0.63. ................................................................................................ 132 

Figure 5.6 - Conductivity, σ (100 kHz) and (b) derivative (dσ/dt) as a function of time for 

cement and BLA and SCBA blended Portland cement pastes. .............................................. 133 

Figure 5.7 - Conductivity, σ (100 kHz) and derivative (dσ/dt) as a function of time for cement 

and BLA and SCBA blended Portland cement pastes. The colors represent the hydration 

periods of Portland cement. The letters A-F indicate the characteristic hydration points and 

the abbreviations TI and TF represent the initial and final of setting time of the paste obtained 

from IS, respectively............................................................................................................... 134 

Figure 5.8 - Variation of the internal temperature of cement and BLA and SCBA blended 

cement pastes. ......................................................................................................................... 137 

Figure 5.9 - Setting time obtained from the Vicat test of the cement and BLA and SCBA 

blended Portland cement pastes. ............................................................................................. 139 

Figure 5.10 - (a) Portlandite content and (b) bound water content of the cement and BLA and 

SCBA blended cement pastes at different hydration periods. The letters A-F indicate the 

characteristic hydration points on the dσ/dt curve. ................................................................. 142 

Figure 5.11 - SEM images of fractured samples of (a)-(b) cement paste, (c)-(d) BLA/25 paste 

and (e)-(f) SCBA/25 paste at 1 and 28 days of hydration (Point C and F, respectively). ...... 143 

Figure 5.12 - BSE images of the polished section of (a) cement paste, (b) BLA/10 paste (c) 

BLA/25 paste, (d) SCBA/10 paste (e) SCBA/25 paste and (f)-(g) EDS mapping of BLA/25 

and SCBA/25 pastes after 28 days of hydration. .................................................................... 144 

Figure 5.13 - Compressive strength of the cement and BLA and SCBA blended Portland 

cement pastes. Different letters represent significant differences between the BLA and SCBA 

blended Portland cement pastes and Portland cement paste considering a significance level of 

5%. .......................................................................................................................................... 146 

 

 
 

 



 

 

TABLES LIST 

Table 2.1 - Nomenclature used in cement chemistry. .............................................................. 25 

 

Table 3.1 - Chemical composition of Portland cement (CPV) (%, by mass). .......................... 64 

Table 3.2 - Summary of the characteristics and key considerations of each region of the σ x t 

and dσ/dt x t curve. ................................................................................................................... 88 

 

Table 4.1 - Chemical composition of cement and RHA (%, by mass). ................................... 94 

Table 4.2 - Beginning and end of each hydration region of cement, RHA/10 and RHA/25 

pastes. ..................................................................................................................................... 103 

Table 4.3 - Characteristic points on the dσ/dt curve of cement, RHA/10 and RHA/25 pastes.

 ................................................................................................................................................ 103 

Table 4.4 - Setting time obtained from the Vicat test and the electrical conductivity curve 

from IS. ................................................................................................................................... 109 

Table 4.5 - Summary of the main considerations of the insertion of RHA in Portland cement 

pastes in each hydration period from the curve σ x t and dσ/dt x t. ....................................... 118 

 

Table 5.1 - Chemical composition, loss on ignition (LOI) (%, by mass) and mean particle 

diameter (Dmean) of Portland cement, BLA, and SCBA. ........................................................ 129 

Table 5.2 - Characteristic points A and B on the dσ/dt curve, maximum temperature and its 

respective time in the temperature test of cement and BLA and SCBA blended cement pastes. 

Characteristic points C, D, E, and F represent the ages of 1, 3, 7, and 28 days, respectively.

 ................................................................................................................................................ 135 

Table 5.3 - Setting time values obtained from the Vicat test and the electrical conductivity 

curve from IS. ......................................................................................................................... 139 



 

 

TABLE OF CONTENTS 

1  INTRODUCTION ........................................................................................................... 16 

1.1  OBJECTIVES ......................................................................................................... 18 

1.2  THESIS STRUCTURE .......................................................................................... 18 

REFERENCES ................................................................................................................... 20 

2  LITERATURE REVIEW ................................................................................................ 22 

2.1 PORTLAND CEMENT ......................................................................................... 22 

2.1.1 Manufacturing process ......................................................................................... 22 

2.1.2 Chemical composition .......................................................................................... 24 

2.1.2.1 Alite (C3S) .................................................................................................... 25 

2.1.2.2 Belite (C2S) ................................................................................................... 25 

2.1.2.3 Tricalcium Aluminate (C3A) ........................................................................ 26 

2.1.2.4 Tetracalcium aluminoferrite (C4AF) ............................................................ 26 

2.1.3 Hydration reaction of Portland cement phases ..................................................... 26 

2.1.3.1 Alite (C3S) .................................................................................................... 27 

2.1.3.2 Belite (C2S) ................................................................................................... 32 

2.1.3.3 Tricalcium aluminate (C3A) ......................................................................... 32 

2.1.3.4 Tetracalcium aluminoferrite (C4AF) ............................................................ 33 

2.1.4 Hydration reaction of Portland cement ................................................................. 34 

2.1.5 Environmental impacts and alternatives ............................................................... 36 

2.2  AGRICULTURAL WASTES AS SCM ................................................................ 39 

2.2.1  Rice husk ash ........................................................................................................ 41 

2.2.2  Sugarcane bagasse ash .......................................................................................... 42 

2.2.3  Bamboo leaf ash ................................................................................................... 44 

2.3  IMPEDANCE SPECTROSCOPY (IS) ................................................................. 45 

2.3.1 Definition and application .................................................................................... 45 

2.3.2 IS data interpretation ............................................................................................ 47 

2.3.3 Electrical conductivity/resistivity obtained from the IS ....................................... 50 

REFERENCES ................................................................................................................... 55 

3 NEW INSIGHTS ON UNDERSTANDING THE PORTLAND CEMENT 

HYDRATION USING ELECTRICAL IMPEDANCE SPECTROSCOPY ........................... 63 

3.1 EXPERIMENTAL PROGRAM ........................................................................... 64 

3.1.1 Materials and Preparation of Cement Pastes ........................................................ 64 



 

 

3.1.2 Test procedure ...................................................................................................... 65 

3.2.2.1 Impedance spectroscopy ............................................................................... 66 

3.2.2.2 Setting Time ................................................................................................. 67 

3.2.2.3 Interruption of hydration processes .............................................................. 67 

3.2.2.4 Thermogravimetric analysis ......................................................................... 68 

3.2.2.5 X-ray diffraction analysis ............................................................................. 69 

3.2.2.6 Scanning electron microscopy ...................................................................... 69 

3.2 RESULTS AND DISCUSSION ............................................................................. 69 

3.2.1 Determination of the optimal frequency range ..................................................... 69 

3.2.2 Characteristic Points on the Electrical Conductivity Curve ................................. 72 

3.2.2.1 Discussion of hydration regions ................................................................... 73 

3.2.3 Correlation of electrical conductivity, % Ca(OH)2, % bound water .................... 86 

3.2.4 Summary of main findings observed using IS ..................................................... 87 

3.3 CONCLUSION ....................................................................................................... 89 

REFERENCES ................................................................................................................... 90 

4 INVESTIGATION OF THE INFLUENCE OF RICE HUSK ASH ON THE 

PORTLAND CEMENT HYDRATION PROCESS USING ELECTRICAL 

MEASUREMENT ................................................................................................................... 93 

4.1 EXPERIMENTAL PROGRAM ........................................................................... 93 

4.1.1 Materials ............................................................................................................... 93 

4.1.2 Samples preparation ............................................................................................. 95 

4.1.3 Test procedures ..................................................................................................... 95 

4.1.3.1 Impedance spectroscopy (IS) ....................................................................... 95 

4.1.3.2 Electrical conductivity of the RHA/water solution ...................................... 97 

4.1.3.3 Setting Time and Compressive Strength ...................................................... 97 

4.1.3.4 Hydration stoppage for XRD, TG/DTG, and SEM analysis ........................ 98 

4.1.3.5 X-ray diffraction analysis ............................................................................. 98 

4.1.3.6 Thermogravimetric analysis ......................................................................... 98 

4.1.3.7 Scanning electron microscopy ...................................................................... 99 

4.2 RESULTS AND DISCUSSION ........................................................................... 100 

4.2.1 Electrical conductivity measurements ................................................................ 100 

4.2.1.1 Discussion of hydration regions ................................................................. 103 

4.2.2 Compressive strength ......................................................................................... 116 



 

 

4.2.3 Summary of main findings of the insertion of RHA in Portland cement paste 

from the electrical conductivity curve obtained by IS. ................................................... 118 

4.3 CONCLUSION ..................................................................................................... 119 

REFERENCES ................................................................................................................. 120 

5 HYDRATION AND MICROSTRUCTURAL EVALUATION OF BLENDED 

CEMENT PASTES WITH POZZOLANS DERIVED FROM AGRICULTURAL WASTES 

USING IMPEDANCE SPECTROSCOPY ........................................................................... 123 

5.1 EXPERIMENTAL PROGRAM ......................................................................... 124 

5.1.1 Materials ............................................................................................................. 124 

5.1.2 Preparation of the pastes ..................................................................................... 124 

5.1.3 Characterization of Portland cement, BLA, and SCBA ..................................... 124 

5.1.4 Characterization of the pastes ............................................................................. 125 

5.1.4.1 Impedance spectroscopy ............................................................................. 125 

5.1.4.2 Setting Time and Compressive Strength .................................................... 126 

5.1.4.3 TG/DTG and SEM measurements .............................................................. 127 

5.2 RESULTS AND DISCUSSION ........................................................................... 128 

5.2.1 Characterization of Portland cement, BLA, and SCBA ..................................... 128 

5.2.2 Electrical conductivity measurements ................................................................ 132 

5.3.2.1 Up to the maximum value of electrical conductivity (Dissolution and 

induction period) ........................................................................................................ 135 

5.3.2.2 After the maximum value of electrical conductivity (Acceleration and 

deceleration period and continuous slow hydration period) ....................................... 137 

5.2.3 TG/DTG and SEM measurements ...................................................................... 141 

5.2.4 Compressive strength ......................................................................................... 145 

5.3 CONCLUSION ..................................................................................................... 146 

REFERENCES ................................................................................................................. 147 

6 GENERAL CONCLUSIONS ........................................................................................ 150 

7 PROPOSALS FOR FUTURE STUDIES ..................................................................... 152 

APPENDIX A – SUPPLEMENTARY MATERIAL OF CHAPTER 3 ............................... 153 

APPENDIX B – SUPPLEMENTARY MATERIAL OF CHAPTER 4 ............................... 161 

APPENDIX C – SUPPLEMENTARY MATERIAL OF CHAPTER 5 ............................... 173 

 



 

 

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1  INTRODUCTION 

Portland cement is the most widely used binder in the world, with an estimated global 

production of more than 4 Gt per year [1,2]. This material has been in use for almost 200 years 

and is obtained from the use of raw materials with sources of calcium and silica, in which are 

calcined at high temperatures (1400-1500 °C) and posteriorly, a source of calcium sulfate is 

added. The hydration of this binder is a process that involves several complex reactions, in 

which it transforms a liquid suspension composed of cement particles and water into a porous 

and durable solid material, known as hydrated cement paste. Since its invention in 1824 by 

Joseph Aspdin, extensive efforts have been made to understand the hydration processes of 

Portland cement, as well as to develop new types of cement with the aim of improving the 

properties of this binder. 

Supplementary cementitious materials (SCMs), which are siliceous, aluminosilicate, or 

aluminosilicate calcium powders, have been used as partial replacements for Portland cement 

[3]. The use of SCMs as a partial replacement for Portland cement has been widely studied 

mainly due to environmental problems associated with the production of Portland cement, 

which is responsible for around 5-8% of global carbon dioxide (CO2) emissions into the 

atmosphere and 12-15% of global energy consumption in industrial activities and benefits in 

terms of mechanical properties and durability [4,5]. Among the SCMs commonly used to 

partially replace Portland cement are industrial byproducts, such as fly ash, silica fume and blast 

furnace slag. However, the search for materials that can be used as SCMs is increasingly 

necessary, since the quantity of SCMs used by the cement industry is not sufficientto supply 

the demand for production of Portland cement, in which predicts an increase of between 12 and 

23% by 2050 [6]. Recent studies have shown that the use of ash from agricultural wastes, such 

as rice husk ash (RHA), sugarcane bagasse ash (SCBA), and bamboo leaf ash (BLA) as SCMs 

have gained attention due to the availability of these wastes, which has increased over the years, 

low cost and promising results in terms of mechanical properties and durability in cementitious 

materials. Furthermore, its insertion in cementitious materials prevents its uncontrolled burning 

and accumulation in landfills, avoiding an even higher environmental problem [7]. It is 

important to highlight that waste reduction in landfills and providing an adequate disposal for 

this wastes is essential to reduce environmental impact and achieve the United Nations 



 

 

17 

 

Sustainable Development Goals for 2030 (SDG-12: Responsible Consumption and Production) 

and the circular economy [8].  

The insertion of agricultural wastes ash into the cementitious matrix modifies the extent 

and hydration reactions of Portland cement, the development of the microstructure and the 

properties of the fresh and hardened state of the cementitious material, acting physically and 

chemically in the hydration process. Therefore, the investigation of these wastes in the Portland 

cement hydration process is essential to understand the several physical-chemical hydration 

reactions involved in the process. 

In relation to the techniques used to understand the hydration process of Portland cement 

pastes, isothermal calorimetry is often used, since the hydration process is associated with the 

release of heat. However, its lack of sensitivity to low heat variations, especially during the 

induction period, does not allow an in-depth understanding of the hydration reactions and 

microstructure formation. Furthermore, calorimetry can present a delay in reading the data to 

reach the equilibrium state (approximately 60 minutes, depending on the temperature), thus 

discarding the data obtained in the first minutes of hydration [9]. Techniques of X-ray 

diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) 

and environmental scanning electron microscopy (ESEM), quasi-elastic neutron scattering 

(QENS), and nuclear magnetic resonance (NMR) are also employed. However, most of these 

techniques are destructive and expensive and some of them require interruption of the sample 

hydration process before analysis, which can modify the morphology and composition of the 

hydrated products. In this way, with the aim of mitigating these effects, the use of electrical 

measurements, in particular, the impedance spectroscopy (IS), has demonstrated effectiveness 

in-situ monitoring of Portland cement hydration processes since 1988 with the first work 

published by McCarter [10]. IS is a non-destructive and sensitive technique that enables 

monitoring in-situ the hydration processes of Portland cement from electrical changes in the 

cementitious material, allowing valuable information to be obtained about physical-chemical 

processes and hydration periods, especially in periods of low heat release (induction period), in 

addition to the evolution of the microstructure.  

Numerous studies have been carried out during the last decade to interpret the complex 

reactions involved in the hydration of Portland cement using electrical conductivity/resistivity 

curves obtained from IS. However, there are still gaps in the understanding of these reactions 

from electrical conductivity curve, requiring further clarification and interpretation of these 

reactions involved during hydration at specific periods in the conductivity curve, mainly in the 



 

 

18 

 

period belonging to the dissolution process and period after the maximum conductivity value. 

Furthermore, there is a huge paucity of studies that address the influence of agricultural wastes 

ash in the Portland cement hydration process (mainly in the early-ages) and studies that use 

electrical conductivity/resistivity curves obtained from IS to study the hydration of Portland 

cement pastes with agricultural wastes. 

 

1.1  OBJECTIVES 

The main objective of this thesis was to study the physical-chemical processes involved 

in the hydration of Portland cement pastes and blended Portland cement pastes with agricultural 

wastes ash (RHA, SCBA and BLA) based on electrical conductivity curves obtained from the 

IS. 

The specific objectives of the research were: 

i) Chemically and physically characterize anhydrous materials; 

ii) Evaluate the influence of hydration processes, the formation and transformation of 

phases of Portland cement pastes and blended Portland cement pastes with RHA, SCBA, and 

BLA from electrical conductivity curves and its derivative obtained from the IS; 

iii) Analyze, and in specific cases, quantify the processes of formation/growth and phase 

transformation of the pastes from the measurements of XRD, TG/DTG, SEM, and time scale 

temperature, correlating these measurements with the electrical conductivity curves and the 

respective derivatives of the pastes; 

iv) Evaluate the setting time of Portland cement pastes and blended Portland cement 

with RHA, SCBA, and BLA from the Vicat test and correlate with the electrical conductivity 

curves and the respective derivatives of the pastes. 

 

1.2  THESIS STRUCTURE 

 The thesis was organized into 7 chapters in order to achieve the proposed objectives of 

the research. 

 Chapter 1 presents an introduction and justification of the research, as well as the 

proposed objectives. 

Chapter 2 presents a review of the literature on Portland cement, which covers the 

manufacturing process, chemical composition and hydration reactions, as well as the 

environmental impacts caused during its production and alternatives to mitigate them. 



 

 

19 

 

Posteriorly, a review of the use of agricultural wastes as SCMs was presented, with higher 

emphasis on the use of RHA, SCBA and BLA. Furthermore, a review of the IS technique 

(definition, application and interpretation of data) and electrical conductivity/resistivity curves 

obtained from the IS of cementitious materials is presented. 

Chapter 3, presented in the form of a paper, addresses new perspectives and 

understandings, as well as to elucidate the behavior of Portland cement hydration through 

electrical conductivity curves obtained by IS.   

Chapter 4, presented in the form of a paper, investigates the influence of RHA on the 

physical-chemical hydration processes of a Portland cement paste through the electrical 

conductivity curve obtained by IS. The paper aimed to contribute to a better understanding of 

the complex effects of RHA on cement hydration reactions, promoting an adequate disposal of 

this waste and the development of a more sustainable cement. 

Chapter 5, presented in the form of a paper, investigates the hydration and 

microstructural evaluation of blended cement pastes with BLA and SCBA through electrical 

conductivity curves obtained by IS. The paper aimed to better understand the complex effects 

of these agricultural wastes on cement hydration, which is not yet fully understood, promoting 

an adequate disposal and technological value to these wastes, aiming at the production of a 

more sustainable cement. 

Chapters 6 and 7 present, respectively, the general conclusions of the main findings 

obtained in the study and the proposals for future work. 

 



 

 

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Figure 1.1 - Structure of the research. 

 

REFERENCES 

[1] A.F. Sosa Gallardo, J.L. Provis, Electrochemical cell design and impedance 

spectroscopy of cement hydration, J. Mater. Sci. 56 (2021) 1203–1220. 

https://doi.org/10.1007/s10853-020-05397-6. 

[2] IEA, Global cement production in the Net Zero Scenario, 2010-2030, (2023). 

https://www.iea.org/data-and-statistics/charts/global-cement-production-in-the-net-zero-

scenario-2010-2030-5260. 

[3] M.C.G. Juenger, R. Snellings, S.A. Bernal, Supplementary cementitious materials: 

New sources, characterization, and performance insights, Cem. Concr. Res. 122 (2019) 257–

273. https://doi.org/10.1016/j.cemconres.2019.05.008. 

[4] M. Ren, T. Ma, C. Fang, X. Liu, C. Guo, S. Zhang, Z. Zhou, Y. Zhu, H. Dai, C. 

Huang, Negative emission technology is key to decarbonizing China’s cement industry, Appl. 

Energy. 329 (2023) 120254. https://doi.org/10.1016/j.apenergy.2022.120254. 

[5] K. Zhang, P. Shen, L. Yang, M. Rao, S. Nie, F. Wang, Development of high-ferrite 

cement: Toward green cement production, J. Clean. Prod. 327 (2021) 129487. 

https://doi.org/10.1016/j.jclepro.2021.129487. 

[6] IEA, Cement technology roadmap plots path to cutting CO2 emissions 24% by 2050, 

(2018). https://www.iea.org/news/cement-technology-roadmap-plots-path-to-cutting-co2-

emissions-24-by-2050. 

[7] B.S. Thomas, J. Yang, K.H. Mo, J.A. Abdalla, R.A. Hawileh, E. Ariyachandra, 

Biomass ashes from agricultural wastes as supplementary cementitious materials or aggregate 

replacement in cement/geopolymer concrete: A comprehensive review, J. Build. Eng. 40 

(2021) 102332. https://doi.org/10.1016/j.jobe.2021.102332. 

[8] T.A. Abdalla, A.A.E. Hussein, Y.H. Ahmed, O. Semmana, Strength, durability, and 

microstructure properties of concrete containing bagasse ash – A review of 15 years of 



 

 

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perspectives, progress and future insights, Results Eng. 21 (2024) 101764. 

https://doi.org/10.1016/j.rineng.2024.101764. 

[9] X. Pang, W. Cuello Jimenez, J. Singh, Measuring and modeling cement hydration 

kinetics at variable temperature conditions, Constr. Build. Mater. 262 (2020) 120788. 

https://doi.org/10.1016/j.conbuildmat.2020.120788. 

[10] W.J. McCarter, S. Garvin, N. Bouzid, Impedance measurements on cement paste, J. 

Mater. Sci. Lett. 7 (1988) 1056–1057. 

 

 

 



 

 

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6 GENERAL CONCLUSIONS 

The study of the hydration processes of Portland cement pastes and blended Portland 

cement pastes with agricultural wastes based on electrical conductivity curves and their 

derivatives obtained by IS was the focus of this work. Based on the experimental program 

carried out this study, the following conclusions can be drawn: 

From the electrical conductivity curve of the cement paste (σ x log t) and its respective 

derivative (dσ/dt) obtained from the IS, eight different hydration regions were identified 

comprising the different hydration periods of Portland cement (see Chapters 3 and 4). A new 

region (region IV) included in the acceleration period was identified and represents the 

resumption of the dissolution reactions and formation of microstructure of the paste, with the 

paste in a semi-fluid state. The shoulder observed in region VI was attributed to the formation 

of AFt phases from the reduction of CaSO4 and secondary ionic release reactions in the pore 

network. Furthermore, it was also possible to establish the initial and final setting time of the 

cement pastes based on the delimitation of region V.  

The slow reduction in σ values, comprised in the continuous slow hydration period 

(Region VIII) is associated with changes in the microstructure that are still occurring in the 

paste (growth of AFt and portlandite phases, transformation of AFt phases into AFm phases, 

densification of C-S-H gel structure and pozzolanic reaction in case of blended cement pastes). 

In the blended cement pastes with agricultural wastes, the dilution effect, water 

absorption by the porous structure of agricultural waste ash and ion adsorption on their surfaces 

were the dominant effect in the early ages of hydration of blended cement pastes. Furthermore, 

a delay in the hydration reactions in the blended cement pastes was observed due to the 

displacement of the σ x log t and dσ/dt curves, prolonging the induction period and setting time 

of the blended cement pastes in relation to the cement paste. 

The blended cement pastes with agricultural wastes showed a less expressive increase 

in σ values in relation to the cement paste throughout the cement dissolution and induction 

periods and was related to the existence of a competitive process between the release of ions 

into the solution due to the dissolution process and the absorption of water in the pores of the 

agricultural waste ash, in addition to the adsorption of ions by the ash surface. 

The highest σ value obtained in the blended cement pastes in the deceleration period 

was related to the lower amount of cement in the mixture, the low pozzolanic reactivity of the 



 

 

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agricultural waste ash in the early ages and possible release of water absorbed by the porous 

structure of the ash. 

SCBA blended cement pastes showed the higher delay in hydration reactions (higher 

extension of induction period and setting time) in relation to other pastes, which is mainly 

associated with the dilution effect and the higher LOI content and particle size of SCBA. 

In relation to the mechanical behavior of the pastes, RHA blended cement pastes and 

BLA/10 paste showed compressive strength results similar to Portland cement paste after 28 

days, showing that the dilution effect was compensated by the filler effect and chemical effect 

of the RHA and BLA. 

Finally, IS proved to be a sensitive technique to monitor in situ the hydration process 

and evolution of the microstructure of cement pastes and blended cement pastes with 

agricultural wastes, especially during the early ages, allowing a better understanding the 

hydration reactions and the effects of RHA, BLA, and SCBA on the hydration process of 

Portland cement. Furthermore, the study highlighted a possible disposal for agricultural wastes, 

contributing to circular economy and reduction of greenhouse gas emissions caused by the 

cement industry, as well as the development of more sustainable Portland cement.