Advanced Materials Research Vols. 639-640

Abstract: This paper studied different size-distribution of recycled coarse aggregates by fractal theory. Cement Stabilized Recycled Aggregate Mixture were prepared by different fractal rate aggregate gradations and the unconfined compressive strength at 7 d and 28 d of the materials were tested. The results showed that the unconfined compressive strength at 7 d and 28 d of the materials with recycled coarse aggregate were higher than the one with natural aggregate when coarse aggregate gradations were same. The higher source rock strength of recycled coarse aggregate was, the larger base material strength was. Generally, the increase of fractal dimension is conducive to the growth of strength. The base materials performances of the same fractal dimension were different when the max particle size was different. So the fractal dimension of recycled coarse aggregate must be determined by maximum particle size.

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: It is studied the effect of binder quantity, water binder ratio on properties of self-compacting concrete made with recycled coarse aggregates. It can be prepared C50 self-compacting concrete made with recycled coarse aggregate by adjusting send proportion, binder quantity, and mixing mineral additive. For example, when the binder quantity is 600 kg/m3, water binder ratio is 0.28, the flexural strength and compressive strength at 28 days of self-compacting concrete made with recycled coarse aggregates are 9.07 MPa and 68.47 MPa respectively.

Abstract: An orthogonal experimental design method was adopted for the mix design of high early strength recycled aggregate concrete (HSRAC), and the influence of water-binder ratio, percentage of recycled aggregate(RA）and highly active compound mineral admixture (HACMA) content on the strength of the concrete was discussed. The test results indicated that water-binder ratio was the most principal and significant influencing factor on the strength of HSRAC, regardless of age. An empirical relationship among the strength of HSRAC, the water-binder ratio, the percentage of recycled aggregate and HACMA content was proposed by using multivariate regression analysis. The demand of opening heavy or heavier traffics and rapid repair concrete on strength to HSRAC could be all met.

Abstract: Because of some drawbacks including low strength, poor dimensional stability, low abrasion resistance, easy to crack and other shortcomings, Portland cement concrete was limited to use as a dominant pavement material in highway construction. This paper studied the feasibility of making high performance pavement concrete by adding 20-40% of high-quality composite ultra-fine fly ash (CUFA) technology to achieve high-performance of concrete roads have been studied. The test results indicated that: with cementitious material content of 360~400 kg/m3 and CUFA content of 20% ~ 40%, adding CUFA improved the workability of concrete significantly; in the meantime, the 28d compressive strength was as high as 50 MPa, and the later strength of concrete continued growing. The designed concrete satisfied the requirements of opening to traffic after 3 days after the construction and heavy and extra heavy traffic in 28 days. The durability, especially the abrasion resistance, and the crack-resistance were improved significantly. The designed pavement concrete not only had a good compressive performance for practical engineering but also had good technical, economic, social and environmental benefits.

Abstract: It was tested the strength and wear value of recycled aggregate concrete mixing fly ash, slag, silica fume and double-mixture or three-mixture in deferent age. The results show that the wear value of recycled aggregate concrete mixing 30% fly ash is more than reference concrete at 3days, but can improve final wear-resisting property significantly. The wear value of recycled aggregate concrete mixing 30% double-mixture of fly ash and silica fume is much lower than reference concrete at 3days, and improve early wear-resisting property significantly. The flexural strength of the concrete is 4.26MPa at 3days, which can satisfy the traffic requirement. The wear value of recycled aggregate concrete mixing 30% three-mixture of fly ash, slag and silica fume is lower than reference concrete at 3days, but the declining rate is not significant. It investigates mechanics of double-mixture technique which improves wear-resisting property at the same time.

Abstract: Shrinkage and creep characteristics of concrete are significant factors in the design of prestressed concrete structures. With large scale/span concrete structures developed, the fly ash or other blends are added into high strength concrete to improve the mechanical properties and workability. As a result, the existing shrinkage and creep predicting models have certain limitations. The creep and shrinkage behavior of high strength concrete with fly ash are studied in this paper. Proper predicting model for shrinkage and creep of high strength concrete is recommended. The influence factor of fly ash is proposed as well. These conclusions would be of great useful for structures with fly ash concrete.

Abstract: In order to study the influence of interface bond condition between new and old cement concrete pavement on overlay performance, the three-dimensional finite element model of the airport double-layer pavement was established. The pavement overlay's load stress and deflection were analyzed, the coupling coefficient between new and old cement concrete pavement was calculated based on the bottom of overlay deflection basin shape factor. The results show that the coupling coefficient reflects the degrees of interface bond condition well. Poor interface bond condition increases the overlay's load stress and deflection. The points that more closely distance from the wheels load center, the bigger the pavement overlay's load stress and deflection is. Therefore, more attention should be paid to the interface bond condition during the airport pavement overlay's designs and constructions.

Abstract: Wind tunnel tests of 1:100 rigid model of fish-shaped roof structures were carried out. The mean, fluctuating (RMS) and peak pressure coefficients, the local shape coefficient distributions on fish-shaped roofs were presented and discussed. It was found that negative pressures (suctions) occurred on the most areas on the roofs, and high negative pressure coefficients occurred on the eaves and cantilevered roof parts. When wind flows blew along the corridors under the roofs, the flows enhanced suctions on the surfaces of the roofs, and the suctions on the lower surface were greater than those on the upper surfaces, positive pressures occurred on that area after superposition of wind actions on the two sides. The roof eaves and regions above the corridors experienced the worst RMS pressure coefficients and the worst minimum pressure coefficients. The distribution characteristics of the worst RMS and minimum pressure coefficients were found to be quite similar to those of the mean pressure coefficients. The results obtained from the experimental investigation are expected to be useful in the wind-resistant design of complex roof structures in typhoon-prone regions.

Abstract: Most tall buildings are constructed in the prosperous center of large cities, where is inevitable to be surrounded by many interfering buildings. Wind interference effects among buildings should not be neglected. Therefore, it is necessary to investigate wind interference effects on such tall buildings. Based on the wind tunnel test of rigid model of a tall building, the wind pressure distribution on the building with interfering buildings around it has been researched, the contours of the mean and fluctuate wind pressure coefficients have also been presented. It has been found that shielding effect and channeling effect are significant in the wind interference effects on building. Wind pressure coefficients on side wall and leeward wall of a upstream building may be dramatically changed in case the wake boundary of the upstream building is interfered. The conclusions might be used as reference to structural design and plan.