| Author: | Das, Kunal Krishna |
| Title: | Development of high-performance preplaced aggregate concrete |
| Advisors: | Lam, Siu-shu Eddie (CEE) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Aggregates (Building materials) High strength concrete Concrete construction Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xxii, 182 pages : color illustrations |
| Language: | English |
| Abstract: | Preplaced aggregate concrete ("PAC") is produced by pre-placing coarse aggregates into formwork and then injecting grout to fill in the voids between the coarse aggregates. Grout can be applied in two ways, i.e. gravity process and pumping process. In the gravity process, grout is applied from the top to flow under the action of gravity. In the pumping process, grout is pumped under pressure. Gravity process is limited to PAC having larger-size coarse aggregates. In most places including Hong Kong, size of commonly available coarse aggregates ranges from 10 mm to 20 mm, and this makes the pumping process inevitable. This requires the use of complex pumping equipment for grouting and results in underutilization of PAC, despite its high potentials. Further, to produce PAC using smaller-size coarse aggregates and through gravity process, grout needs to possess high performance such as high flowability and high cohesiveness (i.e. high resistance to bleeding) and this is achievable by optimizing the grout mix proportions. For delivering a user-friendly approach towards the production of PAC, it is essential to investigate the feasibility of producing PAC with readily available resources, such as regular or smaller-size coarse aggregates and possible exclusion of pumping equipment. Incorporation of supplementary cementitious materials such as ground granulated blast furnace slag (GGBS) and silica fume (SF) in PAC can improve and impart desirable properties to PAC. Hence, experimental investigations were conducted to determine the effect of grout mix proportion, coarse aggregate size, and grouting process on mechanical properties and durability of PAC, for its sustainable application to repair works and small-scale constructions. Experimental results have demonstrated that PAC can be produced successfully via gravity process, using traditional cement-sand grout with coarse aggregate size of 20 mm, displaying compatible performance to that of pumping process. For efficient penetrability of the grout through the coarse aggregate skeleton, flowability of the grout needs to be regulated within a suitable range (efflux time less than 20 seconds). In terms of supplementary cementitious materials, GGBS enhances the flowability of grout, whereas SF improves the compressive strength of grout. By optimizing the composition of SF and GGBS, grout with suitable flowability and acceptable strength can be produced. GGBS and SF enhance the resistance to chloride ion penetration. PAC incorporating GGBS and SF (especially 40% GGBS and 10% SF) displays improved resistance to chloride ion penetration, and this is ascribed to high cement replacements. Given that production of cement alone contributes to the third-largest anthropogenic emission of CO2, successful utilization of industrial by-products like GGBS and SF to form PAC helps to reduce the carbon footprint. In terms of drying shrinkage, low shrinkage PAC specimens can still be produced with incorporation of GGBS and SF. While exclusion of sand from the grout improves the flowability and strength of grout, it reduces the strength, durability, and dimensional stability of PAC. With significant improvement in flowability of grout with the removal of sand, water to binder ratio and coarse aggregate size can be reduced. This subsequently improves the properties of PAC. An empirical relationship to predict the compressive strength of PAC is proposed through experimentally derived factorial design and statistical analysis of collectively obtained data and profound literature review. |
| Rights: | All rights reserved |
| Access: | open access |
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