Search

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]

With rapid urban development, natural aggregate resources have become scarce and a large number of ageing buildings are being demolished, which has resulted in a significant reduction in natural resources and a large increase in construction waste. Therefore, the reuse of solid waste, including waste powder and recycled aggregate, has attracted more and more attention. Additionally, as a prominent way to alleviate the urban heat island effect and manage stormwater runoff, pervious concrete has been widely studied and applied. In this paper, the effects of waste powder (fly ash, volcanic powder and blast furnace slag) and recycled aggregate (recycled concrete aggregate and recycled brick aggregate) on the mechanical properties, water permeability, water filtration and durability of pervious concrete are summarized and introduced, and some prospects are put forward. From the literature review, it can be found that adding the appropriate amount of solid waste or applying proper treatment methods to solid waste will not bring negative effects; rather, it would even improve the performance attributes of pervious concrete. Therefore, the use of solid waste in pervious concrete has great potential for urban construction and environmental protection. [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]

The fine portion of crushed old concrete is difficult to be recycled for use in new concrete because it contains old cement paste, which generally has high porosity and low strength. Hence, in practice, the coarse portion is recycled as coarse aggregate and the fine portion is mostly not recycled. Nevertheless, attempts have been made in recent years to recycle the fine portion as waste concrete powder (WCP) by grinding before use. In this research, WCP was used to make pervious concrete. The WCP was added using the paste replacement method (PR method) of replacing an equal volume of cementitious paste. A series of pervious concrete mixes containing 100% recycled coarse aggregate and having different amounts of WCP added were produced for testing of interconnected porosity, water permeability and strength. The results showed that the addition of WCP using the PR method can improve the interconnected porosity by 9% and water permeability by 18%, greatly enhance the strength by 86%, as well as decrease the cement consumption by 10% at the same time. Therefore, the addition of WCP as paste replacement has great potential to be applied to the production of eco-friendly high-performance pervious concrete. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Cementitious paste samples proportioned with blended ordinary Portland cement, pulverised-fuel ash and condensed silica fume (CSF), with different water/cementitious materials ratios and varying superplasticiser (SP) dosages, were produced for packing density and flowability measurements. The results showed that increasing the SP dosage significantly increased the packing density and water film thickness (WFT) of the cementitious paste, and increases in SP dosage and WFT contributed to increasing the flowability of the cementitious paste. At the same SP dosage and WFT, cementitious pastes containing CSF tended to have higher flowability. It is postulated that this is because the finest portion of CSF and water flowed together as a slurry that coated the larger sized particles with a certain slurry film thickness (SFT). Regression analysis of the test data revealed a very good correlation of flowability to SP dosage and SFT. [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]

Previous studies on the fresh properties of the mortar portion of concrete have revealed that the water film thickness (WFT) is the key factor governing the rheological performance of mortar. However, such studies were limited only to plain mortar containing no fibres. For mortar containing fibres, such as polypropylene (PP) fibres, there have been no similar studies. To investigate the combined effects of WFT and fibre content on the fresh properties of mortar, a number of mortar samples with various water/cement ratios and PP fibre contents were produced for measurements of packing density, flowability, cohesiveness and adhesiveness. It was found that the fibre content has certain effects on the packing density and WFT. Apart from the indirect effects through the change in WFT, the fibre content also has direct effects on the flowability, cohesiveness and adhesiveness. Overall, very good correlations of the fresh properties of mortar to the WFT and fibre content have been obtained and the concept of WFT has been extended to fibre-reinforced mortar. [ABSTRACT FROM AUTHOR]