JOURNAL OF CONCRETE RESEARCH
Year:2019 | Volume:12 | Issue:3 |Papers Count:8

Acidic environments lead to rapid destruction in the reinforcement concrete structures. Chloride ions also lead to rebar corrosion. The aim of this study is to represent an appropriate mortar which resists against each of the acidic and chloride attack. For this purpose, three types of cement with combination of pozzolans (micro silica and pumice/trass) were used as 10 mix designs. Experiments consisted of compressive strength, capillary absorption and water permeability as general tests, and tests which control the performance of specimens against acid attack (compressive strength reduction, weight loss) and chloride attack (surface electrical resistivity, rapid chloride migration test). Results showed that until the age of 240 days, combination of 5% micro silica and 8% trass in slag cement would be an appropriate mix design for mortar against both chloride and acid attack. Usage of 10% pumice as a substitution of trass in the mentioned mix design performed well too.

Nowadays, roller compacted concrete pavement, (RCCP), is becoming popular due to the lower cost of construction, repair, and maintenance compared with those for normal concrete. However, due to the roughness of the RCCP surface, its use in highway roads is limited. In the present paper, the effects of two different compound layers on mechanical and frost resistance of RCCP were investigated. Slag and silica fume as two supplementary cementitious materials were used as a partial replacement for cement in the predetermined mixtures. Hot mix asphalt (HMA) and air-entrained concrete (AEC) were used as compound layer. The mixtures were suffered under freeze-thaw cycles in the present of de-icing salt. The compressive strength and the connection resistance between the compound layers and RCCP after freeze-thaw cycles were evaluated via slant shear and splitting tensile tests. The results indicated that the addition of slag reduced both compressive strength and salt scaling resistance. On the contrary, silica fume improved compressive strength and particularly salt scaling resistance of the specimens. The results also showed that the connection resistance of the specimens was reduced, due to freeze-thaw cycles in the presence of the de-icing agent, about 12% and 10% for HMA and AEC layers, respectively.

Nowadays the use of special and efficient concrete in concrete structures is increasingly spreading due to its unique characteristics. To overcome the issues is to reinforce the concrete by fibers which lead to the formation of multiple micro-cracks that is the main characteristic for providing the tensile ductility of HPFRCC materials. The influence of this material on bending behavior has been studied by many researchers. Thus, its influence on the shear behavior of deep beams is evaluated in this article. For this purpose, the empirical response of five beams including the conventional HPFRCC reinforced deep beams, under concentrated load, in the middle of the span with the shear span to depth ratio of 0. 75 is evaluated. Deep beams of the first group with various fiber percentages of 0, 1 and 2, and, deep beams of the second group with steel fibers of 0 and 2 percent were constructed. The specimens of the first group did not have the web shear reinforcement while specimens of the second group had. After testing the specimens, it was observed that as the percentage of steel fibers increases, the bearing capacity and ductility of the specimens increases as well. Increasing the fiber percentage and adding shear reinforcement increases the shear deformation coefficient. On the other hand, F2 specimens in the second group, which have a shear reinforcement, have a residual coefficient of 9% higher than the same one in the first group (without shear reinforcement).

In this research, the effect of recycled aggregates obtained from the demolition of the old building on the preparation of concrete mixtures has been studied. The purpose of this study was to determine flexural behavior, flexural strength in reinforced concrete beams made of recycled aggregate. In the production of samples, recycled aggregates are used with 0%, 50% and 100% natural aggregates, respectively. The samples were tested for static quadrilateral bending and tested after 28 days of experiment. Therefore, by examining the results of laboratory studies, the flexural behavior of RC beams with the expansion of the recycling has been investigated. In addition, the results are compared with the relationships provided by ACI318, CSA and EuroCode2. The results obtained from this review show that by adding the ratio to the recycled aggregate substitute, the amount of net bending size at the criterial level increases and, with the expansion of the crack extending to the place of loading, the load is released flexibly. In addition, the use of 100% recycled aggregate increases the shape and flexural strength of RC concrete beams.

Copper Mine Tailing (CMT) is a solid-state waste material created through the purification process of copper. Separation of these materials is conducted during the purification Process of copper from copper ores. Since CMT material is an environmental pollutant. The mining enterprises have already been costs a lot for maintenance of these materials. Thus, the disposal of CMT material is a controversial environmental issue which necessitates the reuse/recycle of these materials. Numerous studies have been implemented around the world to dispose these waste materials as partial or complete substitution of fine aggregates or cement in mortars and concrete. This study is aimed at investigating the use of CMT materials as a partial replacement of Ordinary Portland Cement (OPC) in concrete. Specimens were prepared with 0%-30% of CMT material replacement of cement in concrete mixtures. Tests were conducted to determine the mechanical properties of concrete. In addition, the microstructure of cement paste including CMT-materials was investigated using Scanning Electron Microscopy tests. Results revealed that CMT material could be utilized up to 15% as partial replacement of cement. It was observed that CMT concrete (up to 15% substitution) had got improved mechanical properties in comparison to those of OPC concrete at different ages. It is an SiO2-rich material used as the potential source material for all construction projects. The statistical analysis illustrated that properties of CMT concrete were significant at 5% confidence level. Further, the environmental impact was computed and results shown that CMT concrete is more sustainable than control concrete and eco-friendly.

In this research, the robust strength slabs made of concrete, self-compacting, multi-layer reinforced steel and nylon fibers and a combination them under the influence of impact load is investigated. To achieve this goal, 30 concrete slabs one layer and three layers with dimensions 40 40 7. 5 cm are made. The slabs come from 10 different types, one type of non-fibrous as a control, and other slabs all have a fixed volume 1% fiber, hence the type and percentage of fiber varies in the layers. The impact weight loss test was performed on the made slabs. In this test, steel ball weighing 5. 8 kg at a distance 1. 5 m repeatedly hit and The number of blows to make the first crack and the destruction recorded. The results the test indicate a very high effect steel fibers and the slight impact nylon fibers on the slab resistance the slabs. Multi-layered slabs in the firstcracks are the same as the slabs a uniform laminate layer, but the resistance to the destruction and absorption the final energy these slabs increases compared to one-layer samples, which can be due to an increase in the percentage fiber in the outer layers and the layered layout the fibers.

The use of evaporation reducing physical covers in open water reservoirs is one of the most important methods of water conservation. In the present study, three floating cover including Foamthalate, Urthalate and Unoconcrete were designed to protect the water resources of the Sarcheshmeh Copper Complex, which is based on two polystyrene and polyurethane materials. In order to protect the surface layers of the mentioned coatings against the climatic factors and acidic conditions of water was designed concrete liners in 18 concrete mixing designs and the water-to-cement ratio, the amount of Pozzolan replaces cement, Filler and polypropylene fibers was investigated as variable factors. Then the compressive strength of 28 and 42 days of the samples, as well as the corrosion rate within two months, were measured. In the following, the significance of the observed differences obtained from different experiments in samples made was investigated using Duncan's multiple range test. Finally, the results showed that the presence of Isfahan steel slag as a Pozzolan with 45% by weight of cement and the filler of WR780 at a rate of 2% led to get a maximum resistance of 42 days (560 N) and the lowest corrosion rate (4 g) in the L1 experiment. In addition, the results of the L10 and L15 experiments showed that the amount of Pozzolan replacing cement is a very important factor, so that amounts of more than 50% of it, significantly reduces the strength of the concrete and increases the amount of corrosion.

Global water scarcity and air pollution by greenhouse gases have amplified the need to use of unconventional water and environmental friendly materials in the concrete industry. Accordingly, the present study was conducted to investigate interaction of water quality (three levels including including tap water, treated industrial wastewater and the mixture of equal ratio of tap water and treated industrial wastewater), zeolite (four levels including 0, 10, 20 and 30 percent of zeolite application instead of cement in the concrete mix design), cement content (two levels including 250 and 350 kg. m-3) and curing age (including 3, 7, 21, 56 and 90 days) on concrete compressive strength. Regarding to the considerable types of the experimental treatments (120 treatment) in this research and with respect to the lack of statistical analysis in previous studies, the concrete compressive strength data of this study were statistically analyzed by analysis of variance and means comparison tests based on a completely randomized design with factorial experiment with three replications. The results of analysis of variance test showed that the simple effect of the investigated factors, their two-way interactions, except water type*curing age and zeolite *curing age, as well as the three-way interaction of cement content*water type*zeolite on the compressive strength of the concrete specimens were statistically significant. Due to the lack of significant negative effect of treated industrial wastewater and the mixture of equal tap water and treated industrial wastewater on the compressive strength of concrete, it is recommended to use these waters in the construction of plain concrete. However, the three-way interaction of water type with zeolite and cement content showed that the effect of investigated waters on compressive strength of concrete specimens in different percentage of zeolite is depended on cement content. So, the choice of the best application level of zeolite and water type according to the cement content should be selected based on the in-situ mix design test.