Papers by Keyword: Recycled Aggregate Concrete (RAC)

Abstract: An OpenSees computational platform-based 3-dimentional space RAC finite element model is established for reproducing the seismic response of a 1/4 scaled 6-story, 2-bay and 2-span RAC frame model regular in elevation that was tested on shaking table under a series of one-dimensional base excitations with gradually increasing acceleration amplitudes. The dynamic characteristic parameters of the numerical model, including natural frequencies and vibration modes are captured by performed modal analysis. The acceleration response, the maximum storey displacements and the inter-storey drifts are carefully predicted by performed dynamic time history analysis. Very satisfactory agreement between experimental and analytical results is observed. The numerical simulation verifies that the beam-column element type, the section model, the confined concrete model, the steel material model, and the numerical methods used for the proposed model are reasonable.

Abstract: Primary concrete of pebble coarse aggregate were used as the source of recycled aggregate concrete for pebble recycled coarse aggregate. Replacement rate of recycled aggregate for change parameter, 99 specimens were designed. The prism compressive strength, cube compressive strength and flexural strength were tested and achieved. The test results show that damage process and form of pebble coarse aggregate concrete are similar to those of normal concrete. It is gel adhesive failure between coarse aggregate and cement. Comparing with natural aggregate concrete, the strength indexes of recycled aggregate concrete of pebble coarse Aggregate slightly increase.

Abstract: A new type of wall-beam was put forward, of which the upper wall is replaced by recycled aggregate concrete whose coarse aggregate is made of the waste brick. Three recycled aggregate concrete wall-walls and three ordinary brick wall-beams were tested, and then the bearing capacity, stress-strain relationship, cracking load and failure mode were analyzed. The results show that: the structural integrity of recycled aggregate concrete wall-beam is better than ordinary brick wall-beam, and the increase of the depth of joist can improve the mechanical behavior of wall-beam structure under the condition of same depth-span ratio.

Abstract: The experimental investigation of the preparation process of recycled aggregate concrete (RAC) using the waste concrete as recycled aggregate concrete (RCA) was reported. By conducting a series of laboratory experiments, the crushing and sieving procedure of wasted concrete to produce RCA were studied, the RACs with different strengths were designed, the strengths of hardened concrete were investigated. The results indicated that the representative strength for designing C10, C15 and C25 grade RAC using RCA were 11.3, 16.2 and 27.3 Mpa, respectively. The results gained in this study prove to be a valuable building materials using RCA for doveloping the RAC. Recycling and reuse of building wastes have been found to be an appropriate solution to the problems of dumping hundred of thousands tons of debris accompanied with shortage of natural aggregates.

Abstract: This paper presents the experimental results of recycled aggregate concrete filled steel tube columns prepared with different amount of recycled coarse aggregate (RCA) subjected to axial loading. The recycled coarse aggregates are obtained from the earthquake waste in Sichuan. Based on the studying of the physical and mechanical properties of recycled coarse aggregate, the mechanical property of recycled aggregate concrete (RAC) with five concrete mixes with 0%, 25%, 50%, 75% and 100% RCA respectively are prepared. The behaviour of the circular solid steel tube columns are studied in terms of the load carrying capacity, ductility and strain response under axial compressive loading in addition to the physical and mechanical characteristics of RCA and RAC. The results show that the steel tube column gives lower ultimate bearing capacities when the RCA were added. However, no obvious difference on the failure modes were found between the steel tube columns filled with recycled aggregate concrete and normal concrete.

Abstract: The effect of fly ash (FA) and slag (SG) on the anti-cracking performance of recycled aggregate concrete (RAC) is discussed, taking the toughness index as the concrete anti-cracking performance evaluation index, and the mechanism of action is researched at the meantime. The experimental results show that the strength of RAC is reduced when containing fly ash only or slag only, but the crack-resistance of RAC is improved significantly at 3 days and 28 days of hydration process of RAC. Furthermore, the 28 days anti-cracking performance of RCA improved significantly with 30% FA single-doped or 20% SG single-doped .It can improve the 28 days anti-cracking performance of RAC, by using double-mixture of fly ash and slag, there is an optimal FA/SG ratio and a best total content, the FA/SG ratio is 3:1 and the total content is 30%.

Abstract: The wasted cement mortar and internal cracks induced by the secondary breaking process existing on/in recycled aggregates lead to significant reductions in the apparent density, strength and durability of recycled aggregate concrete compared to those of natural aggregate concrete. In this study, recycled aggregate intensification approaches was proposed by removing the old cement mortar from recycled aggregate surface through mechanical agitation, and immersing the recycled aggregate in chemical solutions. A series of laboratory experiments were carried out to validate that the proposed approach could improve various performances of the recycled aggregate, as well as the concrete made of it. The testing results showed that through the combination treatment or modification of mechanical and chemical intensification, both of the compressive and flexural strength of the recycled aggregate concrete could be increased to some extent.

Abstract: To ascertain the dynamic performance of recycled aggregate concrete (RAC) shear walls, four 1/3 scale models, including three mid-rise shear walls with reinforcement ratio 0.25% but different recycled aggregate replacement rate, and one with reinforcement ratio 0.46% and 100% recycled coarse and fine aggregate, were tested on the shaking table. The testing process included elastic, cracking, and failure stage of the models. Dynamic characteristic and dynamic response of models at different stages were studied and the comparison between failure patterns of 4 models was also made. The shaking table test results show that the seismic performance of RAC mid-rise shear wall becomes worse with the increase of the recycled aggregate replacement. And the seismic performance of 100% recycled aggregate concrete shear wall gets a little higher with the increase of the reinforcement ratio.

Abstract: Today, efforts are underway in a number of areas to conserve the environment and protect natural resource. In the construction industry, many researchers have studied the development of new concrete using recycled aggregate (RA). This research proposes a multiple regression model (MRM) for predicting the compressive strength of recycled aggregate concrete (RAC). The compressive strength data of 85 specimens of RAC strengths were used for constructing and evaluating the prediction model. The average error rate of the constructed MRM evaluation is 7.18 percent. This result will be useful for predicting the compressive strength of RAC using multiple regression analysis.

Abstract: Self-compacting lightweight concrete was developed to attain good workability, high compressive strength (at least 50 MPa), minimum cracks, and low specific weight (less than 2000 kg/m3), as well as low elastic modulus (about 30 GPa). The attention was also focused on sustainability of this construction material, which was improved by using in the mixture both GRP industrial by-product as filler and artificial (light expanded clay) or recycled (demolished concrete) as coarse aggregates replacing natural gravel. Satisfactory, if not excellent, results were obtained from the collected experimental data.