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Adding fibers is an effective way to enhance the printability and mechanical performance of 3D printable cementitious materials. Glass fibers are commonly used owing to their sound mechanical properties, high durability and affordable price. However, there is still a lack of systematic and in-depth research on the effects of adding glass fibers to cementitious materials. In this study, a series of 3D printable mortars with varying glass fiber content and water/cement (W/C) ratio were produced to evaluate their printability, flexural strength and compressive strength. The results showed that decreasing the W/C ratio generally has positive effects on printability and mechanical performance, whereas increasing the glass fiber content from 0% to 1% would substantially improve the extrudability, dimensional stability and buildability; increase the flexural strength by up to 82%; but decrease the compressive strength by up to 35%. Such large differences in the effects of glass fibers on the flexural and compressive strengths indicate significant material anisotropy. In fact, comparison of the strength results of printed specimens to those of un-printed specimens reveals that the printing process could increase the flexural strength by 98% but decrease the compressive strength by 47%. [ABSTRACT FROM AUTHOR]

Pervious concrete needs to have many pores to achieve high water permeability, but excessive porosity may cause a serious reduction in strength. Herein, it is postulated that the interconnected porosity and open porosity, which can be separately measured, do not have the same effects on the performance of pervious concrete. To evaluate how the interconnected porosity and open porosity influence permeability and strength, a series of no-fines pervious concrete mixes with varying water/cement (w/c) ratio and paste volume were produced for testing of their interconnected porosity, open porosity, unsubmerged water permeability, submerged water permeability and compressive strength. From the test results, it was found that both the w/c ratio and paste volume have major effects on the porosity, permeability and strength. More importantly, regression analysis showed that the interconnected porosity is the governing factor determining the water permeability, whereas the open porosity and w/c ratio are together the governing factors determining the compressive strength. Lastly, the concurrent strength–permeability performance of the no-fines pervious concrete tested was evaluated. [ABSTRACT FROM AUTHOR]

Recent studies have revealed that the use of limestone fines (LF) to replace an equal volume of cementitious paste in concrete could improve the strength and durability of the concrete and reduce the carbon dioxide footprint of concrete production. However, there are different views on how and why the use of LF as a cementitious paste replacement without changing the mix composition of the paste could increase the performance of hardened concrete, bearing in mind that LF are not inherently cementitious. In this work, the effects of the addition of LF on the packing density and water film thickness (WFT) of concrete mixes were investigated, and the roles of packing density and WFT were studied by correlating the strength and durability to the voids ratio (determined from the packing density) and WFT. Based on the results of this study, it is suggested that the use of LF as a cementitious paste replacement improves strength and durability mainly through increasing the packing density (the same as decreasing the voids ratio) and decreasing the WFT of the concrete mix. [ABSTRACT FROM AUTHOR]