細再生混凝土骨料生產自密實混凝土的可行性研究報告-資料下載頁

　　

【正文】 stability to resist segregation. Therefore, despite all abovementioned technical and environmental advantages, the use of SCC in construction, especially in the USA is still limited owing to the sensitive mixture design and relatively high cost of this technology results from the larger amount of cement and admixtures used in mix design. While SCC has significant environmental advantages in parison to convention concrete due to the absence of noise and vibration during construction, effective and new uses of recycled concrete aggregate (RCA) in cement and concrete industry have also attracted a lot of researchers’ attention from the perspective of environmental preservation and sustainable utilization of resources. Concrete recycling not only conserves virgin aggregate resources, but also reduces unnecessary consumption of limited landfill space, saves energy, reduces greenhouse gas emissions, and actually removes CO2 from the air. It was estimated that the annual worldwide generation of concrete and masonry rubble is approximately one billion tones, while only a small percentage of them are recycled.[2] While local RCA could be successfully used in Portland cement concrete,most of the RCA used currently were only used in less costeffective applications such as backfill, base, and subbase of pavement. More efficient manners of using RCA in construction are in need. Due to concerns of higher fine content and absorption, use of fine recycled concrete aggregates (FRCA) in new concrete is restricted or even prohibited. While it is generally expected that the use of FRCA could have negative impact of concrete properties, such as the decrease in strength and an increase in drying shrinkage rate, there are studies that suggest the use of FRCA is not necessarily inauspicious and it is feasible to obtain concrete with acceptable performancewith FRCA.[3–9] Although using recycled aggregate in concrete has been extensively documented, there are only a limited number researches conducted on SCC with different kinds of recycled aggregate,including recycled concrete, bricks, and glass.[10–21] Different test methods were used to evaluate flowability, passing ability, and stability of fresh SCC, together with harden concrete properties, including pressive strength, tensile strength, and drying shrinkage. Results show that while the performance of SCC is highly dependent on quality of recycled aggregate used in the mix, it is possible to obtain SCC with RCA of acceptable flowability and strength.[13–15] It is also found that most of the works are focused on replacing coarse aggregate, and there is not adequate study on the influence on SCC properties of different rates of FRCA replacement.A systematic research is needed to evaluate performance of SCC with FRCA. The obtained results can be very significant from both technical and environmental prospective.2. Experimental details. Materials Type I Portland cement that meets ASTM C150 (Standard Specification for Portland Cement) [22] and class C fly ash that meets ASTM C618 (Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete) [23] were used as cementitious materials in the concrete mix. The chemical positions and physical properties of cement and fly ash used in the study are reported in Table 1. Crushed limestone, limestonebased manufacturing sand, and silica sand were used as aggregate in the concrete mixtures. RCA with nominal maximum size of 25mm (1 inc.)was obtained from a local recycled concrete plant and further crushed with a laboratory jaw crusher with an opening of approximately 15mm. A sieve was then used to screen out particles larger than the sieve size of (8). FRCA with maximum size of (8) obtained, as shown in Figure 1, was used as substitute of natural fine aggregate, . manufacturing sand and silica sand. Apolycarboxylatebased highrange waterreducing(HRWR) admixture (Glenium174。 7700) and viscositymodifying admixture (VMA) (Rheomac VMA 362) were used to adjust the workability of SCC mixtures. Sieving analyses were performed on all four aggregates used in the study according to ASTM C136 (Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates).[24] Gradation curves of all four different kinds of aggregate are shown in Figure 2. Fineness modulus of manufactured sand, silica sand, and FRCA were calculated as , , and , respectively. Specific gravities and absorptions of aggregates were measured based on ASTM C127 (Standard Test Method for Density, Relative Density [Specific Gravity] [25], and Absorption of Coarse Aggregate) and ASTM C128 (Standard Test Method for Density, Relative Density [Specific Gravity], and Absorption of Fine Aggregate) [26], respectively, and the results are shown in Table 2. It should be noted that due to the high amount of residualhardened cement paste, FRCA has much higher absorption (%) and relatively lowspecific gravity paring to manufactured sand and silica sand.. Mix proportions Two series of SCC mixes as shown in Table 3 were prepared in this study. With series A contains class C fly ash and series B contains only portland cement as cementitious material. The watertocement ratio of series A was and the watertobinder ratio was 。 the watertocement ratio of series B was . Based on the two reference mixes (A FRCA0 and BFRCA0), other eight mixes with FRCA replacement of 25, 50, 75, and 100% (of mass of natural fine aggregate used in reference mixes) were designed to evaluate the effect of FRCA. Since this study is focus on effect of FRCA, in order to simplify the mix design matrix, amount of cement, fly ash, water, HRWR, and VMA were intentionally kept constant within each of these two series. Masses of aggregate used in the table were presented in saturated surface dried conditions.. Concrete mixing A MP 75 SICOMA Laboratory Mixer was used to mix concrete based on procedure as described in AS