Abstract: The paper is one part of ongoing research on structural lightweight aggregate concrete. Lightweight aggregate concrete with compressive strength class of CL40 and slump of 160-200 mm were studied. The influences of the cement content, sand percentage and fly ash dosage on properties of fresh and hardened LWAC, such as fresh density, workability and compressive strength were investigated.
Abstract: The quality of RCA is influenced by the processing method and quality of original
concrete. The general character of RCA, RCA and TR A 0006-2000(concrete using recycled aggregate) are introduced. The execution of RAC work, examples of real constructions with RAC, recycling of concrete powder originated from production of RAC and barriers of using RAC are discussed.
Abstract: The developments of recycled aggregate concrete pressing hard in construction activities; however, the limitations on their applications had never being ended. The focus of this paper is: i) investigating the waste management strategy in construction; ii) proposing the two-stage mixing approach (TSMA) to improve the quality of RAC; and iii) experimenting the TSMA and assessing the benefits possibly gained. It proposes a new approach in mixing concrete, namely, the two-stage mixing method, to improve compressive strength of RAC and lower its strength variability. The replacement ratio from zero to thirty is under experiment on their compressive strength. Based upon the experimental results, improvements of 31 % in strength at 28 days with 30 % RA substitute was achieved. The effect can be attributably to the porous nature of the RA and the pre-mix process which can make some pores filled up resulting in a denser concrete and thus leading to higher
strength when compared with the traditional mixing approach. Therefore, two-stage mixing approach can open up a wider application of recycled aggregate concrete.
Abstract: The subject of concrete recycling is regarded as very important in the general attempt for sustainable development in our times. Due to a wide range of variability of engineering properties for recycled concrete, a large number of experiments are usually required to decide a suitable mixture. Within the scope of this study, 13 different concrete mixtures were manufactured. The amount of recycled concrete aggregate (RCA) were 0 %, 20 %, 40 %, 60 %, 80 %, and 100 %, respectively. The replacement levels of ultra-fine fly ash are 0 %, 15 %, 25 %, 35 % and 50 %, respectively. The physical and mechanical properties along with their workability of concrete produced with RCA and ultra-fine fly ash were investigated. The experiment results showed that ultra-fine fly ash replacement had an important effect on performance of concrete with different amount of RCA.
Abstract: The influence of aggregate to cement ratio(A/C), sand to aggregate ratio(S/A) and water to cement ratio(W/C) on mechanical properties and pervious coefficient of pervious concrete prepared by recycled aggregate were systematically investigated in the paper. The optimum mix proportion by weight of pervious concrete prepared by recycled aggregate were 3.5 of aggregate to cement ratio, 0.15 of sand to aggregate ratio and 0.34 of water to cement ratio, resulted from an effect coefficient method. Flexural strength and compressive strength of pervious concrete road brick prepared by recycled aggregate concrete could satisfy the requirements of Chinese Standard for Concrete Road Brick (JC/T466-2000) and had good pervious performance.
Abstract: With increasing number of melting-solidification plants for the domestic wastes and
incineration ashes, the resulting molten slag is now expected as a recycled aggregate for concrete in Japan, while application examples until now are limited to non-loadbearing pre-cast concrete and concrete secondary products. This study deals with a full-scale application of molten slag recycled fine aggregate. Starting with
the inspection of monthly variations in quality of molten slag fine aggregate in a plant, construction of a full-scale structure was attempted using the recycled aggregate concrete with a superplasticizer. During construction, pumpability of the recycled concrete was examined and the quality of hardened concrete in the structure was evaluated. It was shown that quality variation of the molten slag fine aggregate during eight months was sufficiently small, and pumpability as well as concrete quality in structure showed no significant difference with those of the ordinary concrete.
Abstract: The objective of this investigation is to evaluate the effect of surface treatments on
cement-based materials, which include mortar and concrete samples. Penetrated sealers and methyl methacrylate (MMA) were used as surface treatment materials. Two concrete mixes (w/c = 0.35, 0.55) were selected and cubic/cylindrical specimens were prepared according to ASTM specifications. The treated specimens have higher compressive strengths than the control specimens. Also, the absorptions and total charge passed of rapid chloride penetration test (RCPT) are lower in the treated specimens. Scanning electronic microscope (SEM) was utilized to estimate the microstructure of the specimens. Denser pore structures and narrower pore-size distribution were observed in SEM micrographs and mercury intrusion porosimetry (MIP) spectrum for the treated specimens, which are correspondent to the macro-observation. The positive effect is most prominent in polymer treated specimens. For higher w/c ratio mix, large capillary pores were filled by most of treatment materials and compressive strength significantly increased, while, for lower w/c ratio mix, polymer and silicate sealer filled in medium capillary pores as indicated by MIP and RCPT results.
Abstract: This paper researches on the feasibility of preparing ultra-high strength & high
performance concrete with low quality fine aggregate, such as super fine sand (fineness moduls≤1.10), chippings and manufactured sand. The results shows: with low quality fine aggregate, ultra-high strength & high performance concrete can be prepared, and with excellent fluidity and a compressive strength range of 70~120 MPa.