Full Replacement Of Natural Aggregates Research Articles

A high‐strength concrete resistant to elevated temperatures using steel slag aggregates

AbstractThis paper investigates high‐strength concrete (HSC) exposed to high temperatures using the full replacement of natural aggregates with steel slag. Polypropylene (PP) and steel fibers are used as reinforcements, and the effects of calcium aluminate cement and ordinary cement on the mechanical properties of this concrete are compared. A total of 81 cylindrical specimens of 100 × 200 mm and 81 prism specimens of 100 × 100 × 350 mm were made using different amounts of cementitious materials (cement and silica fume) of 450, 500, and 550 kg/m3, with constant water‐to‐cementitious materials ratio of 0.28. The present results revealed that the HSC made with steel slag aggregates and calcium aluminate cement reinforced with steel fibers, had the greatest compressive strength of 84 and 50 MPa at temperatures of 20°C and 800°C, respectively; and flexural strength of 7.9 and 4.5 MPa, respectively, at the same temperatures. Similar HSC specimens constructed with ordinary cement, on the other hand, performed better at 400°C. Moreover, the flexural strength of the samples placed at temperatures of 400°C and 800°C decreased by 28% and 48%, respectively, compared to the specimens at 20°C. Compared to specimens comprised of polypropylene fibers, the fracture energy and displacement of HSC with steel slag reinforced with steel fibers subjected to high temperatures were increased by approximately 100% and 60%, respectively.

Development of environment-friendly and ductile recycled aggregate concrete through synergetic use of hybrid fibers.

The partial or full replacement of natural aggregates with recycled ones can lessen the harmful effects of concrete industry on the environment. Despite offering sustainability benefits, recycled aggregate concrete (RAC) is inherently brittle under tension similar to natural aggregate concrete (NAC). The present study aimed to enhance the ductility of plain RAC by using hybrid fibers. The effect of single and hybrid fibers was studied on the flexural behavior (flexural strength, flexural toughness, residual strength), splitting tensile strength, and compressive strength of RAC. Polypropylene fiber (PPF) and hooked steel fiber (HSF) and hybrid fiber combination (0.85% HSF + 0.15% PPF) were used in RAC and NAC at a 1% volume fraction of concrete. The results showed that RAC with 1% PPF performed poorly compared to the RAC with 1% HSF. RAC incorporating 1% HSF or hybrid HSF-PPF fibers showed overall better performance than plain NAC. A substantial increment in the tensile and flexural strength of RAC was observed with the incorporation singular HSF and hybrid HSF-PPF. Hybrid fibers have higher efficiency than singular HSF in both RAC and NAC. Residual strength, flexural strength, and flexural toughness of RAC with HSF and hybrid fibers were notably higher compared to the conventional plain NAC. The addition of 0.85% HSF + 0.15% PPF is beneficial to the imperviousness of concrete, and it reduced the water absorption capacity of RAC by 6.4%.

Properties of Steel Fiber-Reinforced Alkali-Activated Slag Concrete Made with Recycled Concrete Aggregates and Dune Sand

Reutilizing industrial by-products and recycled concrete aggregates (RCA) to replace cement and natural aggregates (NA) in concrete is becoming increasingly important for sustainable development. Yet, experimental evidence is needed prior to the widespread use of this sustainable concrete by the construction industry. This study examines the performance of alkali-activated slag concrete made with RCA and reinforced with steel fibers. Natural coarse aggregates were replaced with RCA. Steel fibers were added to mixes incorporating RCA at different volume fractions. Desert dune sand was used as fine aggregate. The mechanical and durability properties of plain and steel fiber-reinforced concrete made with RCA were experimentally examined. The results showed that the compressive strength did not decrease in plain concrete mixes with 30 and 70% RCA replacement. However, full replacement of NA with RCA resulted in a 20% reduction in the compressive strength of the plain mix. In fact, 100% RCA mixes could only be produced with compressive strength comparable to that of an NA-based control mix in conjunction with 2% steel fiber, by volume. In turn, at least 1% steel fiber, by volume, was required to maintain comparable splitting tensile strength. Furthermore, RCA replacement led to higher water absorption and sorptivity and lower bulk resistivity, ultrasonic pulse velocity, and abrasion resistance. Steel fiber incorporation in RCA-based mixes densified the concrete and improved its resistance to abrasion, water permeation, and transport, thereby enhancing its mechanical properties to exceed that of the NA-based counterpart. The hardened properties were correlated to 28-day cylinder compressive strength through analytical regression models.

Eco-efficient cementitious composites with large amounts of waste glass and plastic

This paper presents an experimental study, which has been lacking to date, into the properties and applications of waste glass–plastic cementitious (WGPC) composites incorporating recycled aggregates as a full replacement of natural aggregates, with direct application in highly eco-efficient construction components. Detailed experimental assessments of the fresh properties, strength and durability characteristics of such composites are undertaken. Particular focus is given to the mix rationale and optimisation process as well as possible routes of exploitation of such materials in construction elements. The experimental assessments showed that such composite materials meet the strength and durability criteria for direct application in practice. The best balance in terms of strength and workability was achieved for a waste glass-to-plastic aggregate ratio of 92/8. The presence of relatively large amounts of recycled waste glass particles with small sizes acted as secondary hydration products and contributed to achieving an adequate strength of the material. Besides a lower unit weight and superior thermal properties compared with those of conventional concrete, WGPC components have shown a reliable behaviour under vehicle impact loading and potential wider application in sustainable non-structural construction applications.

RETRACTED: Mechanical properties of EAFS concrete after subjected to elevated temperature

Recycling of materials has become a major interest. Recently, the amount of slag deposited in the storage yard adds up to millions of tons/year leading to the occupation of farmland and serious pollution to the environment. Electric Arc Furnace slag (EAFS) is made at 1500–1650 °C having a honey comp shape with high porosity so it is expected to be good at fire resistance. Using EAFS as a partial replacement of the natural aggregate can be considered a good alternative for sustainable construction because its cost is very low. Although the existence of a high void ratio, this slag showed high compressive strength when using it as a partial replacement of natural aggregate in conventional concrete due to its good strength characteristics. This study investigates the behavior of using EAFS as a partial or fully coarse aggregate replacement by weight with different percentages of 0%, 15%, 30%, 50%, and 100% in concrete when subjected to elevated temperatures. Six groups of concrete mixes were prepared using various replacement percentages of slag exposed to different temperatures of 400 °C, 600 °C, and 800 °C for different durations of 1hr, 1.5hr, and 2hr. Evaluation tests of EAFS performance as a partial or full replacement of natural aggregate in concrete were compressive strength, tensile strength, and bond strength. The steel slag concrete mixes showed weak workability lower than the control mix. A systematic increase of almost up to 21.7% in compressive strength, and 66.2% in tensile strength with increasing the percentage of EAFS replacement to 50%. The experimental results showed that EAFS enhances the concrete properties and the fire resistance as confirmed by Thermal Gravimetric Analysis (TGA). The high void ratio and the slag components are the causes of this fire resistance enhancement result in improving the durability of concrete.

Valorization of phosphate mine waste rocks as aggregates for concrete

The phosphate industry produces great amounts of waste-rocks during their mining activities in extraction and beneficiation steps. Waste-rocks are stored immediately on extraction sites or in the vicinity of treatment facilities. Different types of waste-rocks are generated, yet this paper discusses the use of stone-removal waste-rocks as aggregates for concrete. Starting from the chemical and mineralogical composition, those waste-rocks were characterized by different techniques. Common geotechnical tests were performed to assess the aggregates properties. Then, those aggregates were used in concrete formulation as a full replacement of natural aggregates in order to test their mechanical behavior in comparison to a reference concrete, using compressive, flexural and splitting tensile strengths as parameters to evaluate the concrete performance according to the required standards.Those aggregates indicated a 41% Los Angeles coefficient, 43% Micro Deval coefficient and 5.20% Water Absorption coefficient. The WRAM concrete has indicated an average of 12 MPa of compressive strength, 1.3 MPa of flexural strength and 2.65 MPa of splitting tensile strength at 28 days.

Design and thermal evaluation of a social housing model conceived with bioclimatic principles and recycled aggregates

The present work discloses the design and thermal evaluation of single-family houses adapted with bioclimatic principles to tropical climates – the Vila Sustentável complex. The architectural layout of each 2-bedroom unit embraces accessibility measures and bioclimatic strategies for energy-efficiency. The envelope embodies an innovative approach: the full replacement of natural aggregates by processed steelmaking slag in all cement-based composites (mortars, concretes and concrete blocks). These building elements were characterized physically and thermally. Subsequently, the thermal performance of the buildings was evaluated through an energy simulation using the software EnergyPlus. Results indicated that the stack effect designed in the living room promotes high ventilation rates with no energy consumption. The building elements produced with steel slag presented better thermal performance than the conventional ones, due to the high thermal inertia and low thermal conductivity of the slag. In this sense, the passive strategies proposed are replicable and energy-efficient alternatives for tropical countries.

Effect of electric arc furnace steel slag on the mechanical and fracture properties of roller-compacted concrete

Abstract The present study made an effort to investigate effect of partial and full replacement of natural aggregate with the Electric Arc Furance (EAF) steel slag on the mechanical and fracture properties of Roller Compacted Concrete (RCC). Various concrete mixtures containing fine and coarse EAF steel slag were prepared to find out the impact of each part on the performance of RCC mortar and concrete mixture. To investigate mechanical properties of the mixtures specimens of RCC, different tests were performed, including the splitting tensile, compressive, semi-circular bending and three-point bending tests. The Results showed that fine and coarse EAF steel slag had different impacts on the mechanical properties of the RCC. The results showed that for fine aggregate replacement, obtained mechanical responses decreased by increase in the amount of EAF steel slag, which have the high specific surface area. Besides, incorporating the coarse EAF steel slag increased aggregate interlock mostly due to its high angularity and roughness causing to promote the mechanical and fracture properties. The investigated broken aggregate fraction on the fracture face of beams by image processing and pull-off test results confirmed the mentioned findings.

Modelling the Influence of Waste Rubber on Compressive Strength of Concrete by Artificial Neural Networks.

One of the major causes of ecological and environmental problems comes from the enormous number of discarded waste tires, which is directly connected to the exponential growth of the world’s population. In this paper, previous works carried out on the effects of partial or full replacement of aggregate in concrete with waste rubber on some properties of concrete were investigated. A database containing 457 mixtures with partial or full replacement of natural aggregate with waste rubber in concrete provided by different researchers was formed. This database served as the basis for investigating the influence of partial or full replacement of natural aggregate with waste rubber in concrete on compressive strength. With the aid of the database, the possibility of achieving reliable prediction of the compressive strength of concrete with tire rubber is explored using neural network modelling.

Experimental Analysis of MOC Composite with a Waste-Expanded Polypropylene-Based Aggregate.

Polypropylene (PP) is one of the most widely produced types of plastic worldwide, but its recycling is limited. This work presents a study of the utilization of expanded polypropylene (EPP) waste in a magnesium oxychloride cement (MOC) composite usable in the building industry. MOC is formed by mixing magnesium oxide powder and a concentrated solution of magnesium chloride and is characterized by excellent bonding ability to large quantities of different types of aggregates. A developed air-cured MOC composite, where an EPP-based aggregate was used for the full replacement of natural aggregate, was investigated in terms of its basic physical, mechanical, thermal and water resistance properties. The results demonstrate that incorporation of EPP waste greatly improved the thermal insulation properties, while the mechanical resistance was reduced to an acceptable level. The developed MOC composite containing EPP waste can be considered as an alternative thermal insulation material applicable for the construction of floor or envelope construction systems.

Adopting particle-packing method to develop high strength palm oil clinker concrete

Utilization of locally available waste and by-product to replace conventional concrete materials has gained considerable attention over the past two decades. This study is a part of an extensive research program on the characteristics of palm oil clinker (POC) incorporated concrete. In this study, experimental investigation was carried out on incorporating POC as aggregates and filler material in the production of high strength concrete (HSC). Crushed POC were used as partial and full replacement of natural aggregates i.e. fine and coarse. Palm oil clinker powder (POCP) was then incorporated to fill the voids present on the surface of POC particles, while maintaining the other mix constituents. Fresh and hardened properties of the POC concrete with and without POCP were investigated. Substituting coarse aggregate with POC negatively affected the concrete fresh and hardened properties due to POC porous nature. However, the results of the study revealed that incorporating additional POCP as filler material by adopting Particle-Packing (PP) method improved the engineering properties of POC concrete. Therefore, there is a potential towards utilization of POC for many practical construction applications. POC being an environmentally-friendly and a low-cost aggregate can serve as a normal aggregate alternative for future use.

Time-dependent and long-term mechanical properties of concretes incorporating different grades of coarse recycled concrete aggregates

It is now accepted that replacement of natural aggregates in concrete with recycled concrete aggregates obtained from construction and demolition waste is a promising technology to conserve natural resources and reduce the environmental impact of concrete. This paper presents a study on long-term properties of concretes manufactured with recycled aggregates of different parent concrete strengths. A total of six batches of recycled aggregate concretes (RACs) were manufactured. Tests were undertaken to establish the long-term compressive strength, elastic modulus, splitting tensile strength, workability, drying shrinkage, and creep of each batch. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) characterizations were performed to explain the mechanisms behind the observed time-dependent and mechanical properties of RACs. Test parameters comprised the replacement ratio and parent concrete strength of the recycled aggregates used in the preparation of the new concrete mixes. The results indicate that the parent concrete strength of the recycled aggregates significantly affects the time-dependent and long-term mechanical properties of RACs. It is shown that concrete mixes containing lower strength recycled concrete aggregates develop lower mechanical properties and higher shrinkage strain and creep deformation compared to mixes prepared with higher strength recycled concrete aggregates. Normal-strength RAC mixes containing higher strength recycled concrete aggregates develop slightly lower splitting tensile strength at all curing ages but similar compressive strength and elastic modulus in longer term (i.e. over 90 days) compared to those of the control mix. It is also shown that high-strength RACs, prepared with full replacement of natural aggregates with recycled concrete aggregates having a higher parent concrete strength, exhibit time-dependent and long-term mechanical properties that are similar to or better than those of companion natural aggregate concretes.

Mechanical Performance and Durability of Fly Ash Recycled Aggregate Concretes

According to the concept of sustainable development, the environmental load of a building must be evaluated throughout its life cycle, from design to construction, maintenance or repair, demolition, and rubble disposal. Therefore, from a holistic point of view, sustainable construction means designing a reinforced concrete structure with proper durability during a specified service life. This paper discusses the effect of partial and full replacement of natural aggregates by recycled concrete aggregates (RCA) in a fly ash concrete. Engineering properties and durability performance have been examined for mixtures designed with various proportions of the RCA by mass. Results obtained showed that the addition of RCA lowers concrete performance, but the combined use of RCA and fly ash could allow to achieve adequate engineering properties and durability.

Mechanical Properties of High Strength Concrete with Field-Demolished Concrete as Aggregates

Abstract Environmental and economic factors are increasingly encouraging higher value utilization of demolition debris. While the use of recycled concrete aggregate (RCA) is confined mainly to low-grade application, it would be more beneficial if high strength concrete (HSC) can be produced with demolished concrete for new concrete construction. Hence, an experimental study was undertaken to explore the feasibility and potential of using field-demolished concrete as full replacement of natural aggregates to produce HSC, as reported in this paper. The workability of fresh concrete and mechanical properties of hardened concrete made with RCAs were investigated. The preliminary results indicated that HSC with up to 80 MPa of 28-day compressive strength made with field-demolished concrete as coarse aggregate and natural sand as fine aggregate can be obtained with the facilitation of a modified mixing method and the addition of silica fume. By providing a general basis for evaluating demolished concrete as aggregates for HSC, the investigation reported herein should contribute significantly to the understanding of recycled aggregate concrete as a viable option in the HSC construction industry.