Addition of rice husk ash (RHA) is an effective internal curing method to mitigate self-desiccation and autogenous shrinkage of hydrating cementitious materials. Although a certain number of experimental researches on this topic have been carried out, a comprehensive study about numerical simulation of mitigating effect of RHA on autogenous shrinkage of cementitious materials is still scarce. In this study, a numerical model of autogenous shrinkage of rice husk ash blended cement mortar was proposed. The proposed numerical model was based on Pickett model and improved by taking visco-elastic behaviour of rice husk ash blended cementitious materials into account. Final setting time, chemically bound water, compressive strength, internal relative humidity (RH) and autogenous shrinkage of pure Portland cementitious materials and rice husk ash blended cementitious materials were experimentally studied. Liquid absorption capacity and water vapour desorption isotherm of rice husk ash were also measured. The comparison between the simulated and measured autogenous shrinkage showed that the autogenous shrinkage of rice husk ash blended cement mortar can be predicted accurately with the proposed numerical model.

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This study experimentally investigated the effects of surfactants and water-repelling agents on the hydration process, relative humidity, and mechanical properties of Portland cement pastes. Based on the measurement results, the degree of hydration, degree of saturation, capillary tension of autogenous shrinkage, and magnitude of autogenous shrinkage were simulated using a numerical model. In the numerical model, the elastic and creep components of autogenous shrinkage were calculated separately, and the creep component was simulated based on the solidification theory. The simulation results indicated that adding admixtures led to lower degrees of hydration and saturation. The capillary tension of the pure Portland cement was larger than that of the other mixtures. This can be attributed to several factors, including the smaller surface tension of mixtures with surfactants, larger contact angle of mixtures with water-repelling agents, and a lower degree of hydration of mixtures with both admixtures. Analyses of the simulated and measured results for different mixtures also show that creep plays an indispensable role in autogenous shrinkage. Adding a surfactant and a water-repelling agent can effectively mitigate autogenous shrinkage. However, when an excessive amount of water-repelling agent was added, its influence on the mitigation of autogenous shrinkage was insignificant.

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This study aims to predict the autogenous shrinkage of alkali-activated concrete (AAC) based on slag and fly ash. A variety of analytical and numerical models are available for the prediction of autogenous shrinkage of ordinary Portland cement (OPC) concrete, but these models are found to show dramatic discrepancies when applied for AAC due to the different behaviours of these two systems. In this study, a new numerical approach is developed to predict the autogenous shrinkage of alkali-activated slag (AAS) and alkali-activated slag-fly ash (AASF) concrete from the experimental results on corresponding paste. In this approach, the creep of AAS and AASF and the restraining effect of the aggregate are particularly considered. By this approach, a fairly good prediction is obtained. Moreover, the microcracking in paste caused by restraining aggregates is evaluated. The results indicate that AAC is subjected to high tendency of development of microcracking.

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Shrinkage-induced cracking can impair the durability of concrete structures. In the past few decades, this topic has drawn more and more attention. Shrinkage of mortar and concrete is actually the result of the interaction between the shrinking cement paste and the non-shrinking aggregates. In recent years, different models that consider the restraining effect of aggregates, i.e. Series model and Hobbs’ model, have been proposed to predict the autogenous shrinkage of mortar and concrete. However, in these models both aggregate particles and cement paste matrix are considered as elastic materials. In fact, cement paste is not ideally elastic. Creep also plays an important role in autogenous shrinkage of mortar and concrete. In this paper an extended Pickett model, which takes the effect of creep into consideration, is proposed. The autogenous shrinkage of CEM I and CEM III/B cement mortar and concrete is simulated by using this model and compared with the experimental results to evaluate the accuracy of the predictions. The results show that the extended Pickett model can well predict the autogenous shrinkage of mortar and concrete.

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Alkali-activated slag and fly ash (AASF) materials are emerging as promising alternatives to conventional Portland cement. Despite the superior mechanical properties of AASF materials, they are known to show large autogenous shrinkage, which hinders the wide application of these eco-friendly materials in infrastructure. To mitigate the autogenous shrinkage of AASF, two innovative autogenous-shrinkage-mitigating admixtures, superabsorbent polymers (SAPs) and metakaolin (MK), are applied in this study. The results show that the incorporation of SAPs and MK significantly mitigates autogenous shrinkage and cracking potential of AASF paste and concrete. Moreover, the AASF concrete with SAPs and MK shows enhanced workability and tensile strength-to-compressive strength ratios. These results indicate that SAPs and MK are promising admixtures to make AASF concrete a high-performance alternative to Portland cement concrete in structural engineering.

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In recent years more and more attention has been given to autogenous shrinkage due to the increasing use of high-performance concrete, which always contains supplementary materials. With the addition of supplementary materials-e.g., fly ash and blast furnace slag-internal relative humidity, chemical shrinkage and mechanical properties of cement paste will be affected. These properties significantly influence the autogenous shrinkage of cement paste. In this study, three supplementary materials-i.e., silica fume, fly ash and blast furnace slag-are investigated. Measurements of final setting time, internal relative humidity, chemical shrinkage, compressive strength and autogenous deformation of the cement pastes with and without supplementary materials are presented. Two water-binder ratios, 0.3 and 0.4, are considered. The effects of different supplementary materials on autogenous shrinkage of cement paste are discussed.

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This study aims to provide a better understanding of the autogenous shrinkage of slag and fly ash-based alkali-activated materials (AAMs) cured at ambient temperature. The main reaction products in AAMs pastes are C-A-S-H type gel and the reaction rate decreases when slag is partially replaced by fly ash. Due to the chemical shrinkage and the fine pore structure of AAMs pastes, drastic drop of internal relative humidity is observed and large pore pressure is generated. The pore pressure induces not only elastic deformation but also a large creep of the paste. Besides the pore pressure, other driving forces, like the reduction of steric-hydration force due to the consumption of ions, also cause a certain amount of shrinkage, especially in the acceleration period. Based on the mechanisms revealed, a computational model is proposed to estimate the autogenous shrinkage of AAMs. The calculated autogenous shrinkage matches well with the measured results.

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In recent decades, several simulation models have been proposed to predict autogenous shrinkage of cementitious systems. In most of these models, however, only the elastic deformation caused by self-desiccation of the hydrating cement paste is considered. In fact, cement paste is not an ideal elastic material. Also the time-dependent deformation, i.e. creep, has been proposed an important component of autogenous shrinkage, especially at the early age. In this study, a simulation model for autogenous deformation is proposed, which includes an elastic part and a time-dependent part. The time-dependent part of this model is based on the activation energy concept. The capillary tension is considered as the driving force of the autogenous shrinkages. In order to evaluate the accuracy of the prediction with the proposed model, CEM I and CEM III/B pastes are studied in this paper. The simulated autogenous shrinkages are compared with experimental results.

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Concrete is a brittle composite material that easily fractures under tension. Due to the fact that the early-age deformation of the concrete member is restrained by adjoining structures, cracking can occur throughout the concrete prior to application of any load. The cracks would provide preferential access for aggressive agents penetrating in the concrete and then cause corrosion of reinforcement and degradation of concrete. As a result, the service life of concrete structure would be decreased. There are many different types of early-age deformation of concrete, e.g. temperature induced strain, drying shrinkage and autogenous shrinkage. Among these types of early-age deformation, autogenous shrinkage is a consequence of the self-desiccation during the cement hydration process. For a long time autogenous shrinkage was considered negligible compared with drying shrinkage. In recent years, autogenous shrinkage has drawn more and more attention due to the increasing use of concretes with low water-binder ratios. Despite the fact that phenomenon of autogenous shrinkage has been recognized for several decades, the mechanism behind it is still not fully understood and no consensus has yet been reached. Three is a general agreement about the existence of a relationship between autogenous deformation and relative humidity change in the capillary pores of the hardening cement paste. Many simulation models were built based on this relationship to predict the development of autogenous shrinkage. The reliability of these predictions, however, is not always satisfactory. The discrepancy between the measured and calculated autogenous deformation becomes very pronounced at later ages. In those simulation models, cement paste was considered as an elastic material and only the elastic part of autogenous shrinkage was predicted. In fact, cement paste is not ideal elastic material. When a cement paste is subjected to a sustained load, it will deform elastically and continue to deform further with time, which process is known as creep. Creep plays an important role in autogenous shrinkage of hydrating cement paste. The ignorance of creep would lead to an underestimation of the autogenous shrinkage. The aim of this project is to study the autogenous shrinkage of Portland cement pastes and blended pastes with supplementary materials. The autogenous shrinkage is supposed to consist of two parts, elastic part and time-dependent part (creep), which are simulated separately. Based on the autogenous shrinkage of cement pastes, autogenous shrinkage of cement mortars and concretes were simulated by taking the restraining effect of rigid sand/aggregate particles into consideration. @en