review · Materials
Chemical shrinkage acts as an intrinsic factor influencing early-age cracking in concrete, mortar, and paste, serving as the driver for autogenous and drying shrinkage. While chemical and autogenous shrinkage are identical at initial setting, their values diverge as the material hardens. Shrinkage depends heavily on the water to binder ratio and tracks the degree of hydration, with lower water to binder ratios resulting in higher chemical and autogenous shrinkage. Cement composition and the addition of supplementary cementitious materials also modify these properties. For instance, incorporating fly ash reduces both types of shrinkage, whereas slag does not yield the same reduction. Furthermore, evaluating recent studies reveals emerging insights into how fibres, particularly bio-fibres, alter the chemical shrinkage of cement composites, an area previously lacking published investigation.
Cracking in early-stage concrete compromises the structural integrity and durability of buildings and infrastructure. Understanding the precise chemical and physical processes driving material shrinkage helps engineers design more durable concrete mixtures. By knowing how additives such as fly ash, slag, and natural fibres affect shrinkage, the construction sector can reduce structural cracking and improve long-term building performance.
This review provides baseline insights for concrete manufacturers, civil engineers, and materials developers looking to control shrinkage and early cracking. While the broader findings on supplementary materials draw on established experimental data, the incorporation of bio-fibres represents early-stage research. Practical application requires further testing to translate understanding of bio-fibre interactions and mix ratios into industrial concrete production.
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Chemical shrinkage (CS) is an intrinsic parameter that may affect the early age cracking of paste, mortar and concrete. It is well known as the driving force of self-desiccation, autogenous shrinkage (AGS) and drying shrinkage. During the first stage of cement hydration (at the initial setting time), the CS and AGS are equal. In the hardened stages, there is a difference in values between the two shrinkage parameters. This paper is a comprehensive review on CS and AGS, measurement techniques, modeling and prediction of different cementitious systems. Based on the various experimental studies, chemical shrinkage depends on the water to binder ratio (w/b) and is proportional to the degree of hydration. A low w/b ratio leads to high CS and AGS. The composition of cement has an effect on both CS and AGS. Also, incorporating supplementary cementitious materials (SCMs) affects both shrinkage parameters. It is concluded that adding fly ash (FA) to concrete contributes to CS and AGS reductions. However, this is not the case when concrete contains slag. More than 170 references were consulted including 35 which were published after 2020. According to the authors knowledge, there is no published work on the effect of fibers, especially bio-fibers, on the chemical shrinkage of cement-based composites. Therefore, in addition to traditional chemical shrinkage of cementitious systems, this review includes a section on recent papers conducted by the authors on the effect of bio-fibers on the chemical shrinkage of cement composites.
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DOI: 10.3390/ma17020283
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