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Using glass fibres to reinforce cement-based materials (CBMs) has great effects on their fresh behaviours. In addition, the impact of water – particularly the average water film thickness (AWFT) – on the fresh properties of CBMs cannot be ignored. However, the combined effects of glass fibre content and AWFT on the fresh characteristics of CBMs are not satisfactorily understood. Therefore, in this study, mortar mixtures with varying fibre/cement (f/c) ratios and water/cement ratios were prepared and subjected to mini V-funnel tests, mini slump flow tests, stone rod adhesion tests, sieve segregation tests and wet packing tests. The AWFTs of the mortar mixes were also determined. The experimental results indicated that the f/c ratio (fibre content) had a noticeable influence on the fresh properties, packing density and AWFT. Modelling analysis demonstrated strong correlations of the workability, flowability, adhesiveness and cohesiveness with the f/c ratio and the AWFT. In other words, both the AWFT and the fibre content collectively serve as governing factors influencing the fresh behaviours of mortars reinforced with glass fibre. [ABSTRACT FROM AUTHOR]

Underwater three-dimensional (3D) concrete printing has a great potential to be applied in submarine construction, but there tends to be significant dispersion and strength reduction of the printed concrete due to washout by surrounding water. This research tried to overcome such problems by enhancing the washout resistance and strength of the printable concrete. A series of seawater coral sand mortar mixes containing silica fume (SF), nano silica (NS), glass fibers (GF) and/or hydroxypropyl methyl cellulose (HPMC) were produced, printed under seawater, and tested for their underwater printability and mechanical properties. The test results showed that both SF and NS can enhance the washout resistance, extrudability and buildability, and improve the flexural, compressive, and bond strengths. GF has also positive but relatively smaller effects. On the other hand, HPMC can improve the underwater printability and bond strength, but may have adverse effects on the flexural and compressive strengths. GF and HPMC, when added together, could cause difficulties in underwater printing, and thus are incompatible. Nevertheless, the combined addition of SF, NS, and HPMC greatly enhances the underwater printability and mechanical properties. Based on these results, some anti-washout 3D printable mortars for submarine construction were developed. [ABSTRACT FROM AUTHOR]

Waste concrete recycled powder (WCRP) occupies up to 30% of crushed old concrete and is hard to be reutilized due to its high porosity and low cementitious reactivity. Traditionally, the WCRP is reused as cement substitution in mortar/concrete production, but this substitution method has certain disadvantages. In this research, a novel substitution method, called the paste substitution method, was applied by replacing part of the cement paste with WCRP; a total of 28 trial mortar mixes containing WCRP added as either paste substitution or cement substitution were made for evaluation and analysis. By comparing the test results, it could be found that the incorporation of WCRP using the paste substitution method can remarkably enhance the compressive strength by at most 38.3%, densify the microstructure, and meanwhile greatly reduce the cement consumption by at most 26.7%. The cementing efficiency factor of WCRP in compressive strength was calculated for the first time, and its value is 0.289. Regression analysis showed that there exists good correlation between the compressive strength and effective water/cementitious materials (W/CM) ratio. [ABSTRACT FROM AUTHOR]

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]

Though previous studies have indicated that the fresh behaviours of plain mortar/concrete are mainly governed by the average water film thickness (AWFT), whether the concept of AWFT is also applicable to fibrous mortar/concrete still needs to be explored. Furthermore, for fibrous mortar/concrete, it is obvious that the fibres added also have certain effects on the fresh behaviours. In two previous studies on basalt fibre-reinforced mortar (BFRM), the integral effects of the AWFT and fibre dosage as well as the integral effects of the AWFT and fibre length were individually investigated. In this study, a fibre factor (FF) defined as the fibre volume multiplied by the fibre aspect ratio was employed and 24 extra mortar groups were tested. A total of 68 mortar groups were applied in numerical analysis. The results of the regression analysis yielded good correlations of the workability, fluidity, cohesiveness, and adhesiveness of BFRM with the AWFT and FF, suggesting that the AWFT and FF are together the governing parameters controlling the fresh behaviours of BFRM. Hence, the AWFT and FF may be used to develop a model for the fresh properties of BFRM. [ABSTRACT FROM AUTHOR]