Filler technology for low-carbon high performance concrete

Abstract

The advancement of concrete technology for developing high-performance concrete has inadvertently increased the carbon footprint of concrete owing to usage of relatively high cement content. Furthermore, the increasing awareness of the anthropogenic carbon dioxide emission has called for the eminent reduction in cement content of concrete. Hence, it is utmost important to reduce the high cement content and consequently the high carbon footprint of concrete to ensure a sustainable development of concrete technology.

The use of filler technology has shown potential to lower the carbon footprint of concrete. However, this technology is still not fully mature yet and requires more in-depth investigations. Therefore, a systematic approach should be established on assessing these fillers on their suitability for concrete. Firstly, the filler is envisaged to be categorized into two classes, namely fine-size and medium-size fillers, whose particle sizes are finer than 75 µm, and between 75 µm and 1.18 mm, respectively. Then, the two classes of fillers are used as cementitious paste replacement in this study, which is to replace an equal volume of cementitious paste and consequently reduce the carbon footprint of concrete. Limestone fines (LF) is used as fine-size filler whereas ground sand (GS) is used as medium-size filler in this context. LF is used to produce low-carbon high dimensional stability concrete and low-carbon self-consolidating concrete (SCC) at varying water/cementitious materials (W/CM) ratios. Likewise, GS is used to produce low-carbon SCC at varying W/CM ratios. Also, the effects of combined usage of fillers on the production of low-carbon SCC and its robustness has been investigated. Experimental investigations revealed that the use of LF and/or GS as cementitious paste replacement would have little to no negative effect on the flowability, segregation resistance and passing ability of concrete, but would significantly increase the SP demand and drastically decrease the flow rate and strength, particularly at high volume of replacement. Moreover, the passing ability is discovered to be governed by the mortar volume which can be increased by fillers volume without increasing the cementitious paste volume.

In-depth studies revealed that the fine-size filler would improve the packing density of powder content and aggregate but would increase the total surface area of powder content. This would result in the decrease in water film thickness (WFT). The WFT would have significant effects on the SP demand and strength of concrete. On the other hand, the medium-size filler would improve the packing density of aggregate but would increase the total surface area of the aggregate system. This would result in the decrease in paste film thickness (PFT). The PFT would have effects on the SP demand and strength of concrete. Therefore, the changes in WFT and PFT should be noted when using filler technology.

Several concrete mixes with LF and/or GS so developed have demonstrated the potential of filler technology in reducing the high carbon footprint and satisfying the requirements of high performance concrete simultaneously. The findings would serve as a guideline for the application of filler technology in development of low-carbon high performance concrete.