Effect of paste volume on fresh and hardened properties of concrete

Significance 

Concrete is the second to the largest consumed material in the world. Therefore, it is of great importance to probe into the various factors that govern the properties of concrete. Among the factors, water to cement (W/C) ratio has been deemed for long time as the key factor affecting the concrete properties. Apart from it, cementitious paste volume (CPV) also plays an important role, yet limited research has been done to quantify the effects and unveil the mechanism behind.

Dr. S.H. Chu, from The University of Hong Kong, evaluated the effects of CPV on various performance attributes of concrete at both fresh and hardened states. In the research, a volumetric mix design method was utilized and the concept of mortar film thickness (MFT) was introduced so as to overcome some of the challenges encountered in the previous research. This research was published in a renowned research journal, Construction and Building Materials.

Briefly, with the CPV varying between 26% and 32% at two W/C ratios, a series of tests were carried out to evaluate the packing behavior, workability and mechanical properties of compressive strength, flexural strength, splitting tensile strength and Young’s modulus. Such elaborated tests enable the evaluation of CPV quantitatively. It was found that a decreased CPV at given W/C ratio would lead to a decrease in uncompacted wet density while an increase in compacted wet density, during which the cement content was reduced. Regarding the hardened properties, lowering the CPV within the observed range would increase the strength at all curing ages, increase the Young’s modulus and improve the concrete quality. Meanwhile, a decrease in CPV would thin down the MFT and might impair the workability. However, such impaired workability could be more or less restored by increasing the superplasticizer dosage or adding filler. In the research, the mechanisms behind the above phenomena was revealed from the perspective of MFT. Moreover, it can be also inferred that the use of filler, either inert or reactive, as partial replacement of CPV might also yield improved concrete performance.

To sum up, other than the W/C ratio, appropriate attention shall be paid to the tailoring of CPV during concrete production, as it indicates great potentials in improving concrete properties and most importantly reducing the cement consumption. This research shall pave a way for the development of low CPV concrete with enhanced performance and sustainability.

Effect of paste volume on fresh and hardened properties of concrete - Advances in Engineering

About the author

Dr. S.H. Chu (PhD, HKU) is currently a Postdoc Fellow at the University of Hong Kong. Prior to it, Dr. Chu was educated at The Chinese University of Hong Kong, The Hong Kong University of Science and Technology and The University of Hong Kong for engineering and research knowledge and awarded Hong Kong Green Innovation Merit as R&D team member. Dr Chu’s research interest lies in sustainable strain-hardening cementitious composites (SHCC) and its structural applications.

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Reference

Chu, S.H. (2019). Effect of paste volume on fresh and hardened properties of concrete. Construction and Building Materials, 218, 284-294.

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