جستجوی مقالات مرتبط با کلیدواژه « سنگدانه ی بازیافتی » در نشریات گروه « عمران »

In recent years, a new type of fiber-reinforced concrete, consisting of several different types of fibers, known as hybrid fibers reinforced concrete, has attracted the attention of researchers. The aim of this paper for experimental evaluation of the effect of replacement ratio of recycled aggregates with natural aggregates on the mechanical properties of reinforced concrete with hybrid fibers (steel and polypropylene fibers). To this end, reinforced concrete with hybrid fibers with volume fractions of "0.0%" , "0.5%" , and "1%" of steel fibers and "0.0%" and "0.4%" of polypropylene fibers and replacement ratios of "0.0%" , "25%" , and "50%" recycled coarse aggregate of natural coarse aggregates were tested for compressive strength, Brazilian tensile strength, and flexural strength by four-point bending tests. The results show that increasing the replacement ratio of recycled aggregate leads to a decrease in compressive, tensile, and flexural strength. If polypropylene and steel fibers are added to concrete containing recycled aggregates, the compressive, tensile, and flexural strengths of concrete increase, whose steel fibers are more efficient in improving the tensile and flexural strength of concrete than polypropylene fibers. The combination of polypropylene fibers with steel fibers increases energy absorption and increases the flexural toughness of concrete containing recycled aggregates. Moreover, reinforced concrete with hybrid fibers does not disintegrate after breaking, and hybrid fibers play an important role in maintaining the cohesion of concrete.

Geopolymer concrete has been proposed in recent years as a green alternative to conventional concrete, which can reduce the negative environmental effects of Portland cement production. In this study, the effect of three different factors such as metakaolin replacement, Na2Sio3/NaOH ratio and polypropylene fiber percentage on the compressive strength of geopolymer concrete at 7 and 28 days was evaluated. The results showed that with increasing the ratio of sodium silicate solution to sodium hydroxide, the compressive strength of concrete increases significantly up to 22%. Also, in the analysis of the metakaolin replacement per fly ash, it was concluded that with increasing the percentage of metakaolin replacement up to 30%, the compressive strength of the control sample increased to about 14%. Also, as a general result, adding polypropylene fibers up to 1.5% by volume did not have much effect on the compressive strength of geopolymer concrete. Moreover, the mixed designs obtained along with the compressive strength of the specimens were modeled using the artificial neural network and multivariate regression analysis. Based on the training and testing results, the artificial neural network method in the RMSE and MAE semesters with values of 1.998 and 1.5899, respectively, has an acceptable performance compared to the multivariate regression analysis in predicting compressive strength of geopolymer concrete. In addition, the results of sensitivity analysis showed that Na2Sio3 / NaOH and sample age had the most effect and polypropylene fibers had the least effect in predicting the compressive strength of geopolymer concrete.

Recently, there has been an increasing trend toward the use of sustainable materials. Sustainability helps the environment by reducing the consumption of non-renewable natural resources. Concrete – the second most consumed material in the world after water – uses a significant amount of non-renewable resources. Efforts aimed at producing environmentally friendly concrete can play a major role in securing sustainable construction.Candidate technologies for sustainable concrete materials include the incorporation of supplementary cementitious materials (SCMs) as a partial replacement for Portland cement; as well as recycled materials in concrete production. As a result, an experimental investigation was conducted to study the mechanical properties and durability of concrete constructed with 15% and 30% recycled aggregate concrete as well as 10% zeolite. This experimental program consisted of fourteen mix designs. Thecompressive strength,split tensile strength, electrical resistivity and chloride ion penetration of recycled concrete mixes were compared with the conventional concrete. Results of this study show that the zeolite and recycled aggregate concrete increased compressive strength,split tensile strength and electrical resistivity also decreased chloride ion penetration of concrete. To overcome inferior durability andmechanical properties of recycled mixes, zeolite (10%) has been added to recycled mixes. Results of the mixes including both recycled aggregate concrete and zeolite show superior durability (both electrical resistivity and chloride ion penetration) compared with the conventional concrete.

In this research, have been used of Kriging surrogate methods to obtain the mechanical and durability parameters’ estimation models and a very recent meta-heuristic optimization algorithm to obtain the optimum amount of recycled coarse aggregates and cement in the concrete mix to reach an environmentally friendly concrete. Results have shown that the optimum design point in a 70% humidity environment, 3% chloride ion concentration, and a temperature of 23 at high corrosion risk level has been reached at 20.33% and 0.40 of recycled coarse aggregate and water-cement ratio, respectively, in single-objective optimization. In addition to this, multi-objective optimization results have shown that in an environment with a 70% humidity environment, 5% chloride ion concentration, and a temperature of 23 the optimum design point has been obtained at 18.34%, 0.40 of recycled coarse aggregate, and water-cement ratio, respectively, that the same results hadn’t been observed in the single-objective optimization procedure.

This paper presents the results of an experimental study on the properties of environmentally friendly concrete. In the making of specimens, 0%, 15%, and 30% of ordinary Portland cement (OPC) was replaced by recycled concrete powder (RCP) and silica fume (SF). In addition, 0%, 50%, and 100% of natural aggregates (NA) was replaced by recycled concrete aggregates (RCA). In the production of RCA, 3 types of concrete waste with initial strength of 20, 40, and 80 MPa were used. In this study, rheological, mechanical (compressive, splitting tensile and flexural strengths), economic and environmental (GWP) properties of 28 mix designs were investigated. The results showed that the use of RCA and RCP has a negative effect on rheological and mechanical properties. However, the results showed that the use of RCA and RCP has a positive effect on environmental and economic properties. Moreover, the results indicated that the negative effect of RCA can be prevented by increasing the initial strength of RCA, and the negative effect of RCP can be prevented by using SF. Finally, by optimization of mixing designs, it was concluded that it is justified to use 50% of RCA with initial strength of 40 and 80 MPa and 30% of RCP and SF, in terms of rheological, mechanical, economic and environmental properties.

Self-compacting concrete is one kind of concrete under its weight flows and simultaneous with maintaining homogeneity, without need to vibrator can be filled mold and takes the shape of the container. This concrete due to high performance in construction doesn’t have any risk in aggregates separation. Also, self- compacting concrete has high strength and relatively durability. On the other hand, the existence of huge tile waste and sepulture of these waste by ceramic and tile factories indicates the importance of using this secondary product in the other industries, including the construction industry. Also, with apply of waste material environment can be healthy and safe. In present experimental study, firstly the self-compacting concrete mixing scheme was determined. Then, according to the obtained mixing scheme with replacing recycled aggregates with natural particles, samples with 0, 25, 50 and 100 percentages (by volume) have been made. It should be noted water to cement ratio and percentage of high plasticizer are constant. The amount of limestone and silica fume in all of the mixtures have been fixed. In prepared specimen’s slump test to determine efficiency and compression and water-absorbing tests in 3, 7, 14 and 28 days curing have been performed. Results of the present study show generally with increasing waste tile efficiency and compression strength decrease. Although, durability goes up. Also, especially, with replacing 100% of recycled material with exist particles major changes have been observed but up to 75% have not been seen.