Shrinkage Of Cement Paste Research Articles

Chemical Shrinkage of High-Strength / High-Performance Cementitious Materials

Chemical shrinkage is important property of cementitious materials. It is considered the main cause of autogenous shrinkage of high-strength / high-performance concretes, which are made at low water/cement (w/c) ratio. It is generally assumed that chemical shrinkage varies directly as the degree of hydration and is independent of w/c, since it has its origin in the hydration reaction stoichiometry. The methods of measurements of chemical shrinkage, which include dilatometry, pycnometry and gravimetry (buoyancy), are briefly reviewed. The interpretation of the experimental data on chemical shrinkage of hydrating cement paste is revised in the paper. The chemical shrinkage of cement pastes with w/c ratios of 0.45, 0.33, 0.25 and 0.21 was tested by gravimetry method. The degree of hydration of the pastes was determined by thermogravimetric analyzer (TGA). The effect of water/cement ratio on chemical shrinkage of hydrating cement pastes cured in saturated and sealed conditions was established and compared with the literature data.

Effect of temperature rising inhibitor on expansion behavior of cement paste containing expansive agent

The present study aims to examine the mechanism influencing the expansion characteristics of expansive cement paste in presence of different dosages of Temperature Rising Inhibitor (TRI). The expansion of cement pastes showed a higher expansion strain of the OPC-EA mixture with 0.2% and 0.4% TRI in comparison to the reference sample and a decreased shrinkage of cement pastes containing expansive agent (OPC-EA). Meanwhile, dynamic elastic modulus, hydration kinetics, mineral phase compositions and microstructure characterization of hydration products were also investigated by ultrasonic method, isothermal calorimetry, quantitative X-ray diffraction and scanning electron microscope, respectively. The delayed hydration process of expansive agent increases the amount of expansive agent available to react after the setting of cement pastes, resulting in the increased expansion strain of OPC-EA-0.2%TRI sample. The higher expansion strain of OPC-EA-0.4%TRI sample can be attributed to the lower stiffness of cement paste affected by TRI. The results showed that the addition of TRI is the main force in delaying the hydration process of ye’elimite in expansive agent by acting on the formation and morphology of ettringite. The delayed ye’elimite hydration process can be explained by inhibition of the precipitation or/and growth of ettringite.

Investigation on the potential utilization of zeolite as an internal curing agent for autogenous shrinkage mitigation and the effect of modification

This paper presents an experimental investigation on the potential utilization of one natural zeolite as an internal curing agent for mitigation of self-desiccation and the subsequent autogenous shrinkage of cement paste with low w/b ratio (0.25). Incorporation of 20% zeolite by mass leads to higher internal relative humidity (90.4%) during the first 7 d compared to that of control sample (78.1%). It is indicating that the zeolite under investigated shows partially elimination effect on the self-desiccation and the autogenous shrinkage as well based on the time-zero defined by the onset of internal relative humidity drop. To obtain improved internal curing property, attempts have been done to modify the pore structure of zeolite by acid treatment and/or thermal treatment. However, both nitric acid treatment and thermal treatment shows negative effect on the improvement of internal curing property of zeolite. Because nitric acid treatment tends to increase the BET surface area of zeolite by increasing the volume of 2–7 nm pores, and the thermal treatment tends to reduce the porosity rather than to enlarge the pore size of zeolite.

Mitigation of Drying and Carbonation Shrinkage of Cement Paste using Magnesia

Mitigation of Drying and Carbonation Shrinkage of Cement Paste using Magnesia

Role of alcohol-ethylene oxide polymers on the reduction of shrinkage of cement paste

Concrete drying shrinkage is a major practical problem, but it can be ameliorated by means of “shrinkage-reducing agents” (SRAs). Water vapor sorption isotherms and low temperature DSC measurements suggest that alcohol-ethylene oxide polymers (AEOPs) with a better hydrophilic-lipophilic (HL-) balance are present in meso-pores in which water molecules evaporate from 75% RH to 40% RH. Short-term drying shrinkage measurements show that the better HL-balanced AEOPs reduce irreversible shrinkage, which occurs mainly from 75% RH to 40% RH during the first drying. Based on the similarity between corresponding RH regions, it is concluded that the better HL balanced AEOP in relevant meso-pores hinders agglomeration of C-S-H during the first desorption to mitigate the irreversible shrinkage and reduce the first drying shrinkage.

Shrinkage Behavior of Alkali-Activated Slag Cement Pastes

Nowadays, alkali-activated cements (AACs) are the most promising alternatives to ordinary portland cement (OPC). Such cements characterized by better strength and corrosion resistance that determine improved durability of materials based on them. However, the shrinkage of AAC systems is noticeably higher compared with OPC. The purpose of this work was to study the shrinkage behavior of alkali-activated slag cement (AASC) pastes. To improve early age performance of AASCs – OPC and Ca(OH)2, as mineral additives, were added to the designed cement mixtures. The properties, like, flexural and compressive strength of cement mortars, chemical shrinkage, autogenous shrinkage and drying shrinkage of cement pastes were studied. The results showed that the chemical shrinkage, autogenous shrinkage and drying shrinkage at 28 days were between 0.064 – 0.074 ml/g, 4.5 – 7.9 mm/m and 3.3 – 4.9 mm/m, respectively. The relationship between the nature of alkaline components, the type of mineral additives and the shrinkage behavior of cements were discussed.

On the effect of the physical structure of cement on shrinkage of cementitious materials

The physical structure of cement is of pivotal importance in the study of volumetric stability and cracking of concrete. While most of efforts in the category of crack mitigation of concrete have been devoted to the incorporation of sophisticated chemical admixtures into concrete mixtures, less attention has been paid to the fact that the modification of cement structure can be considered as a sustainable solution to this problem. This study aims to investigate the effect of the modification of the physical structure of cement on workability, early-age strength and autogenous shrinkage of cement pastes. The results show that the modification of cement physical structure can be used as a sustainable route to reduce shrinkage of cementitious materials.

Influence of chemical-mineralogical properties of limestone on the shrinkage behaviour of cement paste and concrete made of limestone-rich cements

Shrinkage in concrete structures may lead to cracks which reduce the durability of concrete against aggressive mediums. In prestressed concrete elements shrinkage results in a significant loss of prestressing forces. Limestone-rich cements with limestone contents beyond the values of DIN EN 197-1 were developed in order to reduce the environmental impact of concrete. In this paper, the results of studies on the shrinkage behaviour of cement paste and concrete made of limestone-rich cements up to 70wt.-% are presented. Results indicated that shrinkage of cement paste and concrete with high limestone contents is strongly dependent on the amount and the chemical-mineralogical properties of limestone. In this context, methylene blue value (MB-value) and alkali oxide content of limestone were identified as the key parameters controlling the drying shrinkage of cement pastes. Depending on the type of limestone, concrete samples made of limestone-rich cements had either higher or lower drying shrinkage than reference samples made of CEM I 52.5 R with the same w/c-ratio. However, lower drying shrinkage deformation was observed in comparison to the reference concrete made of CEM I with a comparable compressive strength. Furthermore, it was ascertained that the contribution of the autogenous shrinkage and carbonation shrinkage to the total shrinkage deformation is almost negligible for cement paste and concrete made of limestone-rich cements.

Early age shrinkage and heat of hydration of cement-fly ash-slag ternary blends

This study investigated the early age autogenous and chemical shrinkage of mortars with slag and fly ash obtained by sieving the freshly mixed concrete after mixing. The hydration heat and contents of air voids formed within mortars during cement hydration were also tested using isothermal calorimetry and 1H NMR. The results showed that the decrease of w/b ratio significantly increased the autogenous shrinkage of mortars, which was more significant for the mortars containing fly ash and slag. With the increase of slag and fly ash replacement level, the autogenous shrinkage of cement mortars decreased linearly. At the same w/b ratio the cumulative heat of hydration and autogenous shrinkage of cement pastes have a good linear correlation. The fraction of voids formed during hydration increased significantly with increasing w/b ratio. For samples with high w/b ratio (e.g. 0.4), the volume of air voids was higher than that of autogenous shrinkage, which was lower for sample with w/b ratio 0.3. The chemical shrinkage calculated from air voids and measured autogenous shrinkage can be well correlated to the hydration heat.

Early-age interaction mechanism between the graphene oxide and cement hydrates

The remarkable properties of graphene oxide (GO) make it as an ideal candidate for developing high performance cementitious composites. In this study, it is the first time to investigate the early-age physical adsorption and chemical interactions between the GO and cement hydrates, which have a great influence on the hydration development, microstructures and drying shrinkage of the GO modified cement paste. The experimental results indicated that the addition of GO led to the decreased fluidity of cement paste, resulting from the rapid interaction between the GO and divalent metal cations released from cement hydrates, characterized by Ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy. It was found that 0.08wt% GO improved the cement hydration rate/heat by accelerating the cement dissolution, providing nucleation site and regulating the microstructure of cement hydrates. The GO covered cement hydrates at the hydration of 10min was characterized by scanning electron microscopy. Moreover, the addition of GO restricted the 28-day drying shrinkage of cement paste due to the more compacted microstructures and self-curing effect at the early age. In conclusion, the research finding gives a thorough understanding on early-age interaction mechanism when the GO is immediately mixed with cement particles, and provides a valuable guidance to the sustainable design of GO modified cementitious materials for construction use.

Experimental validation of a framework for hygro-mechanical simulation of self-induced stresses in concrete

An accurate simulation of the internal stresses that develop in concrete structures in service demands the explicit consideration of the internal heat and moisture movements that induce strains, which in turn have the potential to cause relevant internal stresses. Following a previous exploratory work from the authors, in which a thermo-hygro-mechanical simulation framework had been proposed, the present paper focuses on the validation of the proposed methodology through an experimental program targeted to assist prediction of the evolution of bulk drying shrinkage (and the corresponding internal stresses) in three specimens of different sizes. This paper presents the entire experimental program, which involved extensive concrete characterization using three distinct sizes of specimens, namely: moisture diffusion with internal humidity sensors, compressive strength, E-modulus, creep and shrinkage on three distinct specimen sizes. The program also included characterization of cement paste shrinkage, which was accomplished employing a newly proposed methodology based on the use of very thin specimens monitored with a handheld microscope. Finally, the obtained experimental data was used for partial validation of predictive capacities of the above mentioned simulation framework, mostly in regard to the prediction of bulk shrinkage. It is noted that the validation does not focus on thermal modelling, since this is a matter that has been addressed by the authors in previous works.

Drying and carbonation shrinkage of cement paste containing alkalis

In this work, shrinkage performance of ordinary portland cement (OPC) paste containing various alkali salts was characterized at two drying conditions, namely: nitrogen gas and air. The results show that incorporation of alkalis dramatically increases shrinkage magnitude, but reduces shrinkage kinetics of OPC, regardless of source and type of alkalis (e.g. Na+ or K+). The amount of alkalis bound in the solid hydrated phases, rather than the free alkalis remaining in the pore solution, is crucial in controlling the shrinkage performance of OPC. It is suggested that the alkali enrichment in OPC increases the visco-elastic/visco-plastic compliance (reduce creep modulus) of its solid skeleton under drying-induced internal stresses. This phenomenon is likely to be attributed to the alkalis binding in calcium–silicate–hydrate (C–S–H), which promotes the packing of C–S–H nanoparticles. Carbonation results in shrinkage (i.e. carbonation shrinkage) in plain OPC, but expansion in OPC with alkali enrichment. The overall volume change of OPC due to carbonation may be a result of competition between dissolution-induced shrinkage and crystallization-induced expansion.

Influence of modified quartz tailing on strength and autogenous shrinkage of cement pastes

The amount of quartz tailing applied in concrete construction is limited due to the low performances of cementitious materials containing quartz tailing. The aim of this study was to mitigate the autogenous shrinkage and improve the strength of blended cement containing quartz tailing by modifying the interface between the quartz tailing and the cement matrix. In this study, the quartz tailing was modified by calcining the material mixed with carbide slag at 1050°C. The compressive strength, autogenous shrinkage, microstructure and nanomechanical properties of the blended cement pastes containing modified quartz tailing were investigated. The results show that modified quartz tailing particles mainly consist of an inner core of quartz and a β-dicalcium silicate (C2S) layer. Compared to unmodified quartz tailing, modified quartz tailing increases the compressive strength of the blended cement paste and at the same time decreases its autogenous shrinkage. In addition, the nanoindentation modulus and hardness of the interfacial zone between quartz tailing and cement matrix are improved, and the porosity of the blended cement paste is decreased. This can be attributed to the formation of calcium silicate hydrate gel owing to the hydration of the β-C2S contained in the modified quartz tailing, and hence enhancement of the interface microstructure between the quartz tailing and cement matrix.

PROPERTIES OF CEMENT PASTE AND CONCRETE CONTAINING CALCIUM CARBIDE WASTE AS ADDITIVE

This paper assessed the effect of calcium carbide waste (CCW) as additive on the properties of cement paste and concrete. The CCW used was sourced from a local panel beating workshop. It was sundried and sieved through a 75 µm sieve and characterized by X-Ray Fluorescence (XRF) analytical method. The consistency, setting times and drying linear shrinkage of cement paste with CCW addition of 0, 0.25, 0.5, 0.75 and 1.0 %, respectively by weight of cement were investigated in accordance with standard procedures. The slump values of fresh concrete containing CCW as additive and of 1:2:4 mix ratio and water-cement ratio of 0.5 was determined. A total of sixty numbers of 150 mm cubes of hardened concrete were tested for compressive strength at 1, 3, 7, 28 and 56 days of curing in accordance with standard procedures. The concrete compressive strength was also modeled using Minitab statistical software based on linear regression technique. The results of the investigations showed that CCW was predominantly of calcium oxide (95.69 %) and a combined SiO2, Al2O3 and Fe2O3 content of 3.14 %. The addition of CCW in cement decreased drying shrinkage (100 %), initial setting time (78 %) and final setting time (57 %), but increased consistency (14 %) at 1.0 % CCW content. The addition of CCW in concrete also showed slight increase in slump (6.5 %) and increase in compressive strength with increase in CCW additive up to 0.5 % and decrease in compressive strength with further increase in CCW content. The 28 days compressive strength of concrete with 0.5 % CCW content was 6.4 % more than normal, while that of concrete with 1.0 % CCW content was 14.9 % less than normal. The compressive strength model of CCW-concrete was developed with R2 value of 0.830 and could be used to predict concrete compressive strength. http://dx.doi.org/10.4314/njt.v36i1.4

PROPERTIES OF CEMENT PASTE AND CONCRETE CONTAINING CALCIUM CARBIDE WASTE AS ADDITIVE

This paper assessed the effect of calcium carbide waste (CCW) as additive on the properties of cement paste and concrete. The CCW used was sourced from a local panel beating workshop. It was sundried and sieved through a 75 µm sieve and characterized by X-Ray Fluorescence (XRF) analytical method. The consistency, setting times and drying linear shrinkage of cement paste with CCW addition of 0, 0.25, 0.5, 0.75 and 1.0 %, respectively by weight of cement were investigated in accordance with standard procedures. The slump values of fresh concrete containing CCW as additive and of 1:2:4 mix ratio and water-cement ratio of 0.5 was determined. A total of sixty numbers of 150 mm cubes of hardened concrete were tested for compressive strength at 1, 3, 7, 28 and 56 days of curing in accordance with standard procedures. The concrete compressive strength was also modeled using Minitab statistical software based on linear regression technique. The results of the investigations showed that CCW was predominantly of calcium oxide (95.69 %) and a combined SiO 2 , Al 2 O 3 and Fe 2 O 3 content of 3.14 %. The addition of CCW in cement decreased drying shrinkage (100 %), initial setting time (78 %) and final setting time (57 %), but increased consistency (14 %) at 1.0 % CCW content. The addition of CCW in concrete also showed slight increase in slump (6.5 %) and increase in compressive strength with increase in CCW additive up to 0.5 % and decrease in compressive strength with further increase in CCW content. The 28 days compressive strength of concrete with 0.5 % CCW content was 6.4 % more than normal, while that of concrete with 1.0 % CCW content was 14.9 % less than normal. The compressive strength model of CCW-concrete was developed with R 2 value of 0.830 and could be used to predict concrete compressive strength. http://dx.doi.org/10.4314/njt.v36i1.4

Electrochemical impedance spectroscopy (EIS) of hydration process and drying shrinkage for cement paste with W/C of 0.25 affected by high range water reducer

The objective of this paper is to examine the hydration behaviour, fluidity and drying shrinkage of cement paste with lower water-cement ratio (W/C) of 0.25. The electrochemical technique is utilized to assess the evolution of the hydration process of fresh cement pastes with different amount of high range water reducing admixture (HRWR), as well as the fluidity measured by the mini cone method. The experimental results show that HRWR can effectively influence the hydration behaviour of paste. The parameter Rct obtained by Nyquist curves varies as the dosage of HRWR increase from 0.5% to 1.4%, indicating that HRWR indeed has obvious effect on the ability of paste transferring charge, further influence the structure of fresh cement paste. Meanwhile, the parameter of Rct is closely related to the fluidity of fresh cement paste measured by mini cone. Additionally, the drying shrinkage of cement paste increase when the dosage of HRWR changes from 0.8% to 1.4%. The cement paste with 0.8% HRWR has the highest increasement of drying shrinkage at the first 10days. However, the drying shrinkage of cement pastes with 0.8% HRWR has the lowest value at 90days.

Irreversible desiccation shrinkage of cement paste caused by cement grain dissolution and hydrate precipitation

When cementitious materials are dried, internal stresses are generated that lead to desiccation shrinkage, a portion of which is irreversible. Previous research has indicated that, while a cementitious composite is subjected to a state of stress, dissolution of cement grains and precipitation of hydrates can yield irreversible creep strains, and it is hypothesized that the same process can lead to irreversible shrinkage during drying. To evaluate this hypothesis, a computationally implemented model integrating a microstructural evolution model with a finite element calculation routine was utilized. This computationally implemented model is capable of predicting the magnitude of shrinkage deformation of cement paste during drying conditions as a result of cement grain dissolution and hydrate precipitation. From the simulation results, the mechanism of cement grain dissolution and hydrate precipitation can lead to significant shrinkage behavior of cement paste, and it is also a potential mechanism resulting in the irreversible component of desiccation shrinkage at early ages (e.g., while the hydration rate is significant). The predicted irreversible shrinkage decreases with the age at which drying is initiated as a result of the decreasing hydration reaction rate.

Characterizing cement paste containing SRA modified nanoSiO2 and evaluating its strength development and shrinkage behavior

In this study, shrinkage reducing admixture (SRA) was grafted on NanoSiO2 (NS) surfaces to synthesize novel core-shell (NS@SRA) particles and improve dispersion of NS in cement paste. The synthesized NS@SRA was characterized by Fourier transform infrared spectroscopy, dynamic light scattering, and thermogravimetric analysis. A series of tests were performed to investigate the effects of NS@SRA addition on the compressive strength and shrinkage of cement paste. It is found that NS@SRA increases the strength of cement paste, especially at later ages. Unlike conventional NS, which significantly increases autogenous shrinkage of cement paste, addition of NS@SRA does not appreciably affect autogenous shrinkage of the paste at early ages. Based on dispersion and zeta potential measurements of NS and NS@SRA particles in synthetic pore solution, we propose that hydration products around NS@SRA may result in gradual separation of SRA from the core. The released SRA may reduce shrinkage and mitigate cracking of cement composites at later ages.

Microstructure-based modelling of drying shrinkage and microcracking of cement paste at high relative humidity

In order to comprehensively understand the drying behavior of cementitious materials, this paper presents a microstructure-based model to simulate the water evaporation process in capillary pores, the drying-induced deformation of cement paste with free boundary condition and the microcracking of cement paste under constraint. This model is applicable to high relative humidity ranges where the capillary pressure effect quantified by the Kelvin equation is the primary loading stimulus. Mainly two parts of modeling work are carried out. (1) From a microstructure model of cement paste HYMOSTRUC3D, the water evaporation in capillary pores is captured by a multi-step digitalization algorithm. (2) The drying-induced shrinkage deformation and internal microcracking of hardened cement paste with different boundary constraints are simulated by a 3D lattice fracture model. In order to reduce the computational cost, a two-scale modeling regime is employed where the microstructure of cement paste and the nanostructure of C-S-H are incorporated. Experimental test about free shrinkage of cement paste is utilized to validate the model. At last, the model is compared with poro-elastic-mechanical models, and is applied to study the influences of water-to-cement ratio and hydration time on the free shrinkage as well as the influence of constraints on the internal microcracking.

Application of ultrasonic pulse velocity for assessment of thermal expansion coefficient of concrete at early age

Early age deformations, in concrete, may lead to cracking reducing its mechanical properties and service live. Cracking risk analysis is an essential part of a concrete design, and coefficient of thermal expansion of concrete is indispensable for this purpose. In this paper, an approach that utilizes ultrasonic pulse velocity measurements for assessment of thermal expansion coefficient of concrete at the early age is proposed. An expression for the calculation of the coefficient of thermal expansion was derived based on the theory of poromechanics. Free shrinkage and ultrasonic pulse velocity of cement paste with water to cement ratio of 0.33 were measured starting from the casting, in order to validate the formula. The calculated values were in an agreement with the data found in the literature, though the effect of self-desiccation was not captured. In addition, the calculated value of thermal expansion coefficient was used for decoupling of autogenous and thermal shrinkage of cement paste. Decoupled linear autogenous shrinkage was compared to the autogenous shrinkage measured by volumetric method.