Proceedings of the 4 th World Congress on Civil, Structural, and Environmental Engineering (CSEE’19) Rome, Italy – April, 2019 Paper No. ICSECT 121 DOI: 10.11159/icsect19.121 ICSECT 121-1 Effect of Coarse Aggregate Size and Grouting Process on Properties of Preplaced Aggregate Concrete Kunal Krishna Das 1 , Siu Shu Eddie Lam 1 1 The Hong Kong Polytechnic University, Department of Civil and Environmental Engineering Hung Hom, Kowloon, Hong Kong [email protected]; [email protected] Abstract - Preplaced aggregate concrete (PAC) is produced by first pre-placing the coarse aggregates and then injecting a grout to fill in the voids between the aggregates. This study aims to investigate the effects of coarse aggregate size and grouting process on PAC through experimental study. The effect of flowability and compressive strength of grout is explored. A suitable grout mix is then selected to investigate the effect of different coarse aggregate sizes i.e. 14 mm, 20 mm, 37 mm and 45 mm on the properties of PAC. Effect on PAC using two different grouting processes, namely pumping process and gravity process is investigated. Pumping the grout into preplaced aggregates resulted in lesser void ratio and higher compressive strength. Using 20 mm size aggregates for production of PAC is recommended to achieve higher compressive strength and better resistance to chloride ion penetration. Keywords: Preplaced aggregate concrete, Aggregate size, Grouting process, Compressive strength, Durability. 1. Introduction Preplaced aggregate concrete ("PAC") is known by various names such as colcrete [1], polcrete [2], two stage concrete [3], prepacked concrete [4], etc. It is different from normal concrete in two fundamental ways, namely method of construction and mix proportion. Firstly, coarse aggregates are placed into the formwork and grout is applied to fill in the voids. Secondly, the ratio of coarse aggregates in the mix proportion of PAC is higher than that in normal concrete. Typical value is about 60% as compared with 40% in normal concrete [5]. As coarse aggregates are preplaced first, they can occupy 60% to 70% of the total volume. In other words, only 30% to 40% of the total volume of grout is needed on-site. This substantially reduces the wet trades and exploitation of machinery and equipment on-site. Since coarse aggregates are not involved in the mixing process, PAC is environmental friendly with lesser consumption of energy. With a higher content of aggregates, PAC reduces the use of cement by 20% to 30% [6]. This reduction in cement also minimizes temperature rise in PAC. Engineering properties of PAC, including its stress-strain relationship, is governed by the properties of coarse aggregates [7]. Applied stress is received by the skeleton of coarse aggregates and transferred to the hardened mortar [8]. Crushed aggregates showed better compressive strength then rounded aggregates, due to its rough surface, enhancing the mechanical interlock in between the aggregates and the grout [9, 10]. However, the void ratio also increases, resulting in higher consumption of grout per concrete volume. Well-graded aggregates are recommended to minimize these voids. The void content can be reduced to as low as 25% of total volume by combining coarse aggregates with two different grading such as 12 mm and 38 mm and 200 mm and 250 mm [11]. Grout fluidity also affects the void content, as it may impede the grouting process. Dimensions through which the grout will pass is determined by the minimum size of the coarse aggregates used. Generally, the smallest size of coarse aggregates should be at least four times larger than the largest size of fine aggregates [11]. In the past, different sizes of coarse aggregates were suggested. Earlier, the recommended size of coarse aggregates in PAC was 38 mm [12]. The main advantage of being able to use larger size coarse aggregates is a reduction in the cost of crushing. Coarse aggregates smaller than 20 mm were suggested to be eliminated as they may interrupt the grout flow. Neville proposed the use of coarse aggregates of sizes smaller than 38 mm, with the aggregates being gap-graded and of multiple sizes [13]. Later, the minimum size of coarse aggregates of 10 mm was suggested by Orchard [14]. However, the grouting process and the grout determine the minimum size of the coarse aggregates used or vice versa [3].
Effect of Coarse Aggregate Size and Grouting Process on Properties of Preplaced Aggregate Concrete
Jul 01, 2023
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