Using Steel Meshes for Enhancing Bond Response Between Steel Bars and Steel Fibre Reinforced Recycled Aggregate Self-compacting Concrete

Evaluation of the bond behavior of steel reinforcing bars in recycled fine aggregate concrete

The Efficiency of Steel Slag and Recycled Concrete Aggregate on the Strength Properties of Concrete

Bond behavior between recycled aggregate concrete and deformed rebar after Freeze-thaw damage

Influence of different types of fibers on the mechanical properties of recycled waste aggregate concrete

This paper presents the effects of silica fume and steel fiber on the mechanical properties and impact behavior of recycled aggregate concrete containing two types of recycled coarse aggregates (RCAs). In total, 20 series of concretes are considered and they are divided into 4 groups. The first group consisted of 1 control concrete containing natural coarse aggregate and 4 control recycled aggregates concretes containing 50 and 100% RCA of two types (A and B). The second and third series are similar to the first series in every aspect except the former contained 8% silica fume as partial replacement of ordinary Portland cement and the latter contained 1% steel fiber by volume. In the fourth series, both 8% silica fume and 1% steel fiber are used. Compressive and split tensile strengths of all concretes are measured in terms of mechanical properties evaluation and low velocity impact hammer test is conducted to evaluate the impact behavior of all concretes. Results show that the concrete containing RCA obtained from high strength parent concrete exhibited better mechanical properties than that containing RCA made low strength concrete. The addition of silica fume improved the split tensile and compressive strengths of recycled aggregate concretes containing both types of coarse aggregates. The addition of steel fibers significantly increased the compressive and split tensile strengths of all concretes, especially recycled aggregate concretes. The simultaneous use of silica fume and steel fibers had a significant effect on the compressive and split tensile strengths of all recycled aggregate concretes, probably due to better bond of steel fibers with mortar containing silica fume as well as improved ITZ between RCA and mortar. The addition of 100% RCA of both types significantly reduced the impact resistance of recycled aggregate concretes. The same is also true even when silica fume is added. The addition of steel fibers significantly improved the impact behavior of recycled aggregate concretes. The addition of silica fume, however, did not show any significant improvement in impact resistance of steel fiber-reinforced recycled aggregate concretes.

Experimental study on dynamic properties of flax fiber reinforced recycled aggregate concrete

A large volume of concrete debris is being produced in many countries on the globe due to the demolition of old concrete structures and testing of concrete specimens in laboratories. One of the ways to reuse concrete debris is to produce Recycled Aggregates (RA) and use them in new concrete. In recent years, Recycled Aggregates Concrete (RAC) has experienced increasing demand in various non-structural and structural applications. In reinforced concrete structures, one of the sources of brittle failure is sudden loss of bond between reinforcing bars and concrete in anchorage zones. Therefore, for the structural application of any new kind of concrete such as fiber reinforced RAC, knowledge of bond characteristics of reinforcing bars embedded in concrete becomes essential for determining the overall structural response under different modes of loading. In this regard, this study experimentally investigated the effect of fibers on the bond stress-slip behavior of deformed steel re-bar embedded in RAC. Concrete mixes having 0, 50 and 100% RAs were prepared with and without the addition of fibers. Two types of fibers were investigated in mono form: hooked-ends steel and polypropylene fibers. The dosage of steel and polypropylene fibers was kept 40 and 4.4 kg/m3, respectively. Axial compression and standard pull-out tests were performed. Test specimens for pull-out test were prepared using deformed steel re-bars of 19mm (#6) diameter. The results of strength tests confirmed that the compressive strength of concrete is decreased by replacing Natural Aggregates (NA) with RAs. For bond behavior of steel re-bar, the results of this study showed that replacement of 50% NA with RAs did not affect the bond response of steel bar, however, 100% replacement of NA with RAs showed detrimental effect on bond stress slip behavior. The results further showed that the addition of both types of fibers made it possible to recover the loss in compressive strength, bond strengths and bond toughness occurred because of replacing NA with RAs. In case of RA concrete mixes containing hooked-ends steel fibers, strength values were found even greater than the strength values of Natural Aggregates Concrete (NAC). From the results of this study, it was found that it is possible to design a structural concrete mix using 100% RAs and steel fibers at relatively low dosage of 40kg/m3.

Experimental studies on the structural reinforced-concrete shear wall members using recycled aggregate concrete (RAC) have been focusing on static loading conditions. The dynamic tests on the reinforced concrete members made of RAC are fairly few. Shaking table tests are necessary because it is difficult to predict the influence of variations in particular properties on the overall dynamic behaviour of the reinforced RAC shear walls made of various mixed materials. The aim of the research work presented in this paper was to investigate the dynamic behaviour of shear walls made of RAC, with different recycled aggregates and reinforcement arrangements, in comparison with shear walls made of natural aggregate concrete (NAC). Five low-rise shear walls were tested in this project: a shear wall made of NAC, a shear wall made of recycled coarse aggregate concrete, and three shear walls made of recycled coarse and recycled fine aggregate concrete with different reinforcement arrangements. Dynamic characteristics and responses of all specimens at different loading stages were determined experimentally, and a comparison of failure modes was presented. The earthquake response time-history analysis of each specimen was also conducted using the finite element software ABAQUS. The ABAQUS results showed good agreement with the test results. The comparison of results showed that, when the reinforcement arrangement was the same, the seismic performance of the shear wall made of recycled coarse and recycled fine aggregate concrete was weakened greatly compared with that of the shear wall made of NAC. The seismic performance of the shear wall made of recycled coarse aggregate concrete was similar to that of the shear wall made of NAC. The seismic resistance capacity of the shear wall made of RAC could be greatly improved by installing concealed bracings.

This paper presents influence of treatment and mixing methods on recycled aggregate concretes (RAC) designed regarding various techniques. Absolute Volume Method (AVM) according to TS 802, Equivalent Mortar Volume Method (EMV), silica fume (SF) as a mineral addition were considered in the design of concretes. In total, four groups of concretes were produced in the laboratory: (1) natural aggregate concrete (NAC) designed with AVM as control concrete, (2) RAC designed with AVM as control RAC, (3) RAC with SF as a mineral addition designed with AVM as treated RAC and (4) RAC designed with EMV as treated RAC. The tests were performed at 28th days and the statistical analysis were made on the test results. According to the results, EMV and SF increased the compressive strength of concretes and this resulted an increase in the strength class of concrete. A significant statistical difference between the concretes were determined. According to multiple comparison analysis, it was found that especially there was a significant relationship among NAC, RAC and RAC-EMV. In addition, it was recommended that EMV and AVM with 5% SF could be used in the design of RAC rather than AVM only to achieve the target strength class C30/37.

The results of thirty pullout tests carried out on 8 and 10 mm diameter deformed steel bars concentrically embedded in recycled aggregate concrete designed using equivalent mix proportions with coarse recycled concrete aggregate (RCA) replacement percentages of 0, 25, 50, 75 and 100 % are reported towards investigation of bond behaviour of RCA concrete. Bond strengths of the natural aggregate concrete and the RCA concrete was found to be comparable, particularly for the 10 mm rebars, and the RCA replacement percentage had an insignificant effect on peak bond stress values. However, for both the bar sizes, when the measured bond strengths were normalized with the respective compressive strengths, then the normalized bond strengths so obtained across all the RCA replacement percentages were higher for the RCA concrete compared to the natural coarse aggregate concrete. Further, higher normalized bond strength values were obtained for the 8 mm rebars compared to the 10 mm bars. An empirical bond stress versus slip relationship between RCA concrete and deformed steel bars has been proposed on the basis of regression analysis of the experimental data and it is conservatively suggested that anchorage lengths of 8 and 10 mm diameter deformed bars in RCA concrete may be taken the same as in natural aggregate concrete.

Conservation and reuse of resources are important aspects of sustainability. It is common practice in the U.S. to crush old concrete pavements at the end of their service lives into recycled concrete aggregate and then reuse them in the base course of new pavements. It is not, however, common to use the recycled concrete aggregate (RCA) in the new concrete pavement itself. This paper examines the sustainability and, in particular, the economics of using RCA in the construction of new concrete pavements. Life cycle cost analyses were performed for various hypothetical pavement construction scenarios including RCA both in the base and in the concrete layer and compared with conventional options. If RCA is simply substituted for natural aggregate in a concrete mixture, the concrete is likely not to perform as well as a concrete made without RCA. This can be compensated for by decreasing the water–cement ratio and/or increasing the cement content. Despite this fact, the results of the life cycle cost analyses show that it can be very economical to use RCA in new concrete pavement construction. As the natural aggregate used for concrete may be more expensive than the natural aggregate used for base courses, it may make good economic sense to substitute RCA for natural aggregate in concrete. Life cycle analysis also shows that concrete with RCA may have better environmental impact.

Recycled construction and demolition concrete waste as aggregate for structural concrete

Mechanical and durability performance of recycled aggregate concrete incorporating low calcium bentonite

A comparative study of the life cycle assessment of natural, recycled, and oil palm shell aggregate concretes

The amount of construction and demolition waste has increased considerably over the last few decades due to growing construction industries. There has been an increasing trend toward the use of sustainable materials and reduce the consumption of non-renewable natural resources. Recycling and reuse of demolition concrete in construction is one potential solution to minimise the natural resources. Recently the main use of recycled concrete aggregate (RCA) is for non-structural applications such as in road sub-bases. However, research studies suggest that the natural aggregates can be partially or fully substituted by RCA if well graded and good quality RCA is guaranteed. The RCA concrete has a lower elastic modulus, compressive and tensile strength, and ductility and greater water absorption than natural aggregate (NA) concrete. Furthermore, the age of the concrete used as RCA has a vital effect on the mechanical properties of the recycled aggregate concrete. However, adding steel fibres (SFs) into RCA mix may improve its mechanical properties. The purpose of this study is to evaluate the percentage of RCA replacement and the age of original concrete on the compressive and tensile strength RCA at 7-, 14- and 28- days. Furthermore, this research will investigate the effect of steel fibre percentage and hook geometry on the compressive and tensile strength of NA to anticipate the effect of steel fibres on the mechanical properties of concrete made from RCA. To achieve that, a number of concrete cubes, cylinders with different percentage of RCA replacements and 3D and 5D hooked end SFs are casted to assess the compressive and tensile strength.