Effect of microsilica addition on compressive strength of rubberized concrete at elevated temperatures

An experimental investigation was carried out to study the effects of various percentages of fine/coarse tire waste and microsilica at various temperatures on the compressive strength of concrete. The compressive strength of concrete mixtures made with tire rubber was assessed statistically with those of concrete containing microsilica and conventional concretes in order to evaluate the usefulness of recycling rubber waste as a component of concrete. Results confirmed that the recipe and processing temperature of concrete cubes influence the compressive strength values. Generally, the use of microsilica or fine rubber mixed with microsilica as aggregate replacement of 5% by volume improved the compressive strength of concrete processed at a temperature of 150°C. The addition of coarse rubber did not achieve any increase in strength when used as an aggregate replacement at any percentage. Moreover, the reductions in the compressive strength of concrete mixes at higher temperatures were much smaller for the fine rubber with 5 vol% microsilica than those for control and coarse rubber mixes. The specimens made with fine rubber and 5 vol% microsilica at elevated temperatures above 400°C appeared to show very similar compressive strength values. The use of fine rubber in building construction could help save energy and reduce costs and solve the solid waste disposal problem posed by this type of waste.     

Evaluating the strength development of mortar using clinker fine aggregate with a combination of fly ash and its inhibitory effects on alkali–silica reaction and delayed ettringite formation

The aggregate composed of cement clinker, an intermediate cement product, improves strength development and mass transfer resistance of concrete. Fly ash (FA) is a supplementary cementitious material that can be substituted by cement. This study investigated the strength development of highly FA-substituted mortar mixed with cement clinker fine aggregate (CL) and tested its inhibitory effect against the alkali–silica reaction (ASR). In addition to these, this study provides the testing results of evaluating the effects of using cement clinker fine aggregate on delayed ettringite formation (DEF), which can be problematic for precast concrete products. The study results revealed that at 91 days of age, in the case of 80% replacement ratio of fly ash to cement, using CL exhibited similar strength development as mortar with limestone fine aggregate and no FA substitution. Furthermore, mortars with 70% and 80% FA substitution did not exhibit clear ASR-induced expansion even at 182 days of age. Lastly, mortar using clinker fine aggregate could suppress DEF-induced expansion at 182 days of age, which was similar to the effect obtained using FA. These results can promote the utilization of CL resources for concrete and using clinker as fine aggregate in precast concrete products.

     

Compressive strength and resistance to chloride ion penetration and carbonation of recycled aggregate concrete with varying amount of fly ash and fine recycled aggregate

Construction and demolition waste has been dramatically increased in the last decade, and social and environmental concerns on the recycling have consequently been increased. Recent technology has greatly improved the recycling process for waste concrete. This study investigates the fundamental characteristics of concrete using recycled concrete aggregate (RCA) for its application to structural concrete members. The specimens used 100% coarse RCA, various replacement levels of natural aggregate with fine RCA, and several levels of fly ash addition. Compressive strength of mortar and concrete which used RCA gradually decreased as the amount of the recycled materials increased. Regardless of curing conditions and fly ash addition, the 28 days strength of the recycled aggregate concrete was greater than the design strength, 40 MPa, with a complete replacement of coarse aggregate and a replacement level of natural fine aggregate by fine RCA up to 60%. The recycled aggregate concrete achieved sufficient resistance to the chloride ion penetration. The measured carbonation depth did not indicate a clear relationship to the fine RCA replacement ratio but the recycled aggregate concrete could also attain adequate carbonation resistance. Based on the results from the experimental investigations, it is believed that the recycled aggregate concrete can be successfully applied to structural concrete members.     

Properties of lightweight aggregate concrete prepared with PVC granules derived from scraped PVC pipes

This paper aims to investigate the fresh and hardened properties of lightweight aggregate concretes that are prepared with the use of recycled plastic waste sourced from scraped PVC pipes to replace river sand as fine aggregates. A number of laboratory prepared concrete mixes were tested, in which river sand was partially replaced by PVC plastic waste granules in percentages of 0%, 5%, 15%, 30% and 45% by volume. Two major findings are identified. The positive side shows that the concrete prepared with a partial replacement by PVC was lighter (lower density), was more ductile (greater Poisson's ratios and reduced modulus of elasticity), and had lower drying shrinkage and higher resistance to chloride ion penetration. The negative side reveals that the workability, compressive strength and tensile splitting strength of the concretes were reduced. The results gathered would form a part of useful information for recycling PVC plastic waste in lightweight concrete mixes.     

Manufacture of artificial aggregate using MSWI bottom ash

This paper reports the results of an investigation on material recovery by stabilization/solidification of bottom ash coming from a municipal solid waste incineration plant. Stabilization/solidification was carried out to produce artificial aggregate in a rotary plate granulator by adding hydraulic binders based on cement, lime and coal fly ash. Different mixes were tested in which the bottom ash content ranged between 60% and 90%. To avoid undesirable swelling in hardened products, the ash was previously milled and then granulated at room temperature. The granules were tested to assess their suitability to be used as artificial aggregate through the measurement of the following properties: density, water absorption capacity, compressive strength and heavy metals release upon leaching. It was demonstrated that the granules can be classified as lightweight aggregate with mechanical strength strongly dependent on the type of binder. Concrete mixes were prepared with the granulated artificial aggregate and tested for in-service performance, proving to be suitable for the manufacture of standard concrete blocks in all the cases investigated.     

Waste tyre rubberized concrete: Properties at fresh and hardened state

The main objective of this paper is to investigate the properties of various concrete mixtures at fresh and hardened state, obtained by a partial substitution of coarse and fine aggregate with different volume percentages of waste tyres rubber particles, having the same dimensions of the replaced aggregate. Workability, unit weight, compressive and flexural strength and post-cracking behaviour were evaluated and a comparison of the results for the different rubcrete mixtures were proposed in order to define the better mix proportions in terms of mechanical properties of the rubberized concrete. Results showed in this paper were also compared to data reported in literature. Moreover, a preliminary geometrical, physical and mechanical characterization on scrap tyre rubber shreds was made.The rubberized concrete mixtures showed lower unit weight compared to plain concrete and good workability. The results of compressive and flexural tests indicated a larger reduction of mechanical properties of rubcrete when replacing coarse aggregate rather than fine aggregate. On the other hand, the post-cracking behaviour of rubberized concrete was positively affected by the substitution of coarse aggregate with rubber shreds, showing a good energy absorption and ductility indexes in the range observed for fibrous concrete, as suggested by standard (ASTM C1018-97, 1997).     

Experimental study of rubber tire aggregates effect on compressive and dynamic load-bearing properties of cylindrical concrete specimens

Sustainable development has become a major focus for engineers and planners as part of their collective efforts in finding, developing and integrating environmental-friendly solutions for material recycling and waste management into design and construction of civil engineering infrastructure. In the past three decades, there has been an increase in recycling and application of waste materials into the concrete to decrease costs and improve material properties of the concrete. Significant growth in automobile manufacturing industry and increased rubber tire supply for vehicles suggested the application of waste tire particles as concrete aggregates to minimize the ecological footprint of the rubber tire waste due to its recycling process difficulties. In this paper, the effect of rubber tire particles on compressive and dynamic strength of concrete specimens with different particle percentiles was tested on more than 55 cylindrical specimens. To achieve the optimal mix design properties of rubber tire concrete specimens, both fine and coarse aggregates got replaced by fine and coarse rubber particles. Introduction of rubber tire particles as coarse and fine aggregate reduces the brittleness of the concrete and provides more flexible aggregate bonding which ultimately improves the dynamic resistance of the concrete. It increases the concrete workability and provides environmental-friendly and cost-effective solutions in using recycled materials for concrete construction applications.     

Properties of alkali-activated systems with stone powder sludge

This article investigates the effects of stone powder sludge on the microstructure and strength development of alkali-activated fly ash and blast furnace slag mixes. Stone powder sludge produced from a crushed aggregate factory was used to replace fly ash and granulated blast furnace slag at replacement ratios of 0%, 10%, 20%, and 30% by mass. The unit weight and compressive strength of the samples were measured, and scanning electron microscopy/energy dispersive spectroscopy and X-ray diffraction (XRD) analyses were performed. The test results indicated that the compressive strength of alkali-activated blast furnace slag mixes using stone powder sludge was higher than that of the alkali-activated blast furnace slag control mix, but the compressive strength of alkali-activated fly ash mixes decreased with increasing replacement ratio of stone powder sludge. Microscopy results indicated that for alkaliactivated blast furnace slag samples, broken surfaces were more evident than for the alkali-activated fly ash samples. For all XRD diagrams, broad and diffuse peaks were observed around 2θ = 35° (d = 2.96–3.03 Å), implying amorphous or short-ordering structure phases.     

High fire resistance in blocks containing coal combustion fly ashes and bottom ash

Fire resistance recycled blocks, containing fly ash and bottom ash from coal combustion power plants with a high fire resistance, are studied in this paper by testing different compositions using Portland cement type II, sand, coarse aggregate and fly ash (up to 50% of total weight) and bottom ash (up to 30% of total weight). The fire resistance, physical-chemical (density, pH, humidity, and water absorption capacity), mechanical (compressive and flexural strength), and leaching properties are measured on blocks made with different proportions of fly ash and bottom ash. The standard fire resistance test is reproduced on 28 cm-high, 18 cm-wide and 3 cm-thick units, and is measured as the time needed to reach a temperature of 180 °C on the non-exposed surface of the blocks for the different compositions.The results show that the replacement of fine aggregate with fly ash and of coarse aggregate with bottom ash have a remarkable influence on fire resistance and cause no detriment to the mechanical properties of the product. Additionally, according to the leaching tests, no environmental problems have been detected in the product. These results lead to an analysis of the recycling possibilities of these by-products in useful construction applications for the passive protection against fire.     

全废砖再生轻骨料混凝土试验研究

将废粘土砖加工成粗细骨料,用于配制全废砖再生轻骨料混凝土.检测结果表明：所用废砖粗细骨料属轻骨料范畴,但其吸水率较大,且细骨料级配不良.试验表明：本试验配合比体系中,净水灰比为0.42,体积砂率为50％时最佳;以全废砖配制的再生砖轻骨料混凝土的强度发展规律与普通轻骨料混凝土类似,均有随水泥用量提高而强度提高的趋势,但随着所配制的混凝土强度等级的提高,再生轻骨料混凝土的强度提高趋势下降.以全废砖为骨料适合配制强度等级LC30及以下的再生轻骨料混凝土.     

双掺粉煤灰再生骨料对混凝土强度影响研究

通过试验研究再生骨料混凝土中粉煤灰和再生骨料对混凝土强度的影响。采用粉煤灰替代部分水泥、再生骨料替代部分天然粗骨料的方法,通过正交试验测定混凝土立方体抗压强度的方法,来研究粉煤灰对再生骨料混凝土强度的影响。试验得出:当再生骨料掺量为20%~30%时,粉煤灰的最佳掺量为20%左右;当再生骨料掺量高于40%、粉煤灰掺量高于20%时,其混凝土拌合物搅拌时间不小于240 s,且当粉煤灰在20%~30%时,可获得较理想的混凝土抗压强度;当粉煤灰的掺入量分布在20%~30%、再生骨料的最佳掺量为50%时,可获得较理想的混凝土抗压强度。由此得出,合理的再生骨料、粉煤灰掺量对混凝土的抗压强度影响并不明显且有提高的趋势,对降低混凝土成本,提高建筑垃圾的再生利用,有一定的经济效益和社会效益。     

Value-added utilisation of recycled concrete in hot-mix asphalt

The feasibility of partial substitution of granite aggregate in hot-mix asphalt (HMA) with waste concrete aggregate was investigated. Three hybrid HMA mixes incorporating substitutions of granite fillers/fines with 6%, 45% untreated, and 45% heat-treated concrete were evaluated by the Marshall mix design method; the optimum binder contents were found to be 5.3%, 6.5% and 7.0% of grade Pen 60/70 bitumen, respectively. All three hybrid mixes satisfied the Marshall criteria of the Singapore Land Transport Authority (LTA) W3B wearing course specification. The hybrid mix with 6% concrete fillers gave comparable resilient modulus and creep resistance as the conventional W3B mix, while hybrid mixes with higher concrete substitutions achieved better performance. X-ray diffraction (XRD) showed the distinct presence of free lime in the heat-treated concrete, while the scanning electron microscope (SEM) provided an in-depth perspective of the concrete grains in the HMA matrix. The results suggest feasible use of waste concrete as partial aggregate substitution in HMA.     

Promoting the use of crumb rubber concrete in developing countries

The use of accumulated waste materials in third world countries is still in its early phases. It will take courage for contractors and others in the construction industry to recycle selected types of waste materials in the concrete mixes. This paper addresses the recycling of rubber tires accumulated every year in Jordan to be used in concrete mixes. The main objectives of this research were to provide more scientific evidence to support the use of legislation or incentive-based schemes to promote the reuse of accumulated waste tires. This research focused on using crumb tires as a replacement for a percentage of the local fine aggregates used in the concrete mixes in Jordan. Different concrete specimens were prepared and tested in terms of uniaxial compression and splitting tension. The main variable in the mixture was the volumetric percentage of crumb tires used in the mix. The test results showed that even though the compressive strength is reduced when using the crumb tires, it can meet the strength requirements of light weight concrete. In addition, test results and observations indicated that the addition of crumb rubber to the mix has a limited effect toward reducing the workability of the mixtures. The mechanical test results demonstrated that the tested specimens of the crumb rubber concrete remained relatively intact after failure compared to the conventional concrete specimens. It is also concluded that modified concrete would contribute to the disposal of the non-decaying scrap tires, since the amount being accumulated in third world countries is creating a challenge for proper disposal. Thus, obliging authorities to invest in facilitating the use of waste tires in concrete, a fundamental material to the booming construction industry in theses countries, serves two purposes.     

Recycling of waste glass as a partial replacement for fine aggregate in concrete

Waste glass creates serious environmental problems, mainly due to the inconsistency of waste glass streams. With increasing environmental pressure to reduce solid waste and to recycle as much as possible, the concrete industry has adopted a number of methods to achieve this goal. The properties of concretes containing waste glass as fine aggregate were investigated in this study. The strength properties and ASR expansion were analyzed in terms of waste glass content. An overall quantity of 80 kg of crushed waste glass was used as a partial replacement for sand at 10%, 15%, and 20% with 900 kg of concrete mixes. The results proved 80% pozzolanic strength activity given by waste glass after 28 days. The flexural strength and compressive strength of specimens with 20% waste glass content were 10.99% and 4.23%, respectively, higher than those of the control specimen at 28 days. The mortar bar tests demonstrated that the finely crushed waste glass helped reduce expansion by 66% as compared with the control mix.     

Possibility of using waste tire rubber and fly ash with Portland cement as construction materials

The growing amount of waste rubber produced from used tires has resulted in an environmental problem. Recycling waste tires has been widely studied for the last 20 years in applications such as asphalt pavement, waterproofing systems and membrane liners. The aim of this study is to evaluate the feasibility of utilizing fly ash and rubber waste with Portland cement as a composite material for masonry applications. Class C fly ash and waste automobile tires in three different sizes were used with Portland cement. Compressive and flexural strength, dry unit weight and water absorption tests were performed on the composite specimens containing waste tire rubber. The compressive strength decreased by increasing the rubber content while increased by increasing the fly ash content for all curing periods. This trend is slightly influenced by particle size. For flexural strength, the specimens with waste tire rubber showed higher values than the control mix probably due to the effect of rubber fibers. The dry unit weight of all specimens decreased with increasing rubber content, which can be explained by the low specific gravity of rubber particles. Water absorption decreased slightly with the increase in rubber particles size. These composite materials containing 10% Portland cement, 70% and 60% fly ash and 20% and 30% tire rubber particles have sufficient strength for masonry applications.     

Properties of concrete blocks prepared with low grade recycled aggregates

Low grade recycled aggregates obtained from a construction waste sorting facility were tested to assess the feasibility of using these in the production of concrete blocks. The characteristics of the sorted construction waste are significantly different from that of crushed concrete rubbles that are mostly derived from demolition waste streams. This is due to the presence of higher percentages of non-concrete components (e.g. >10% soil, brick, tiles etc.) in the sorted construction waste.In the study reported in this paper, three series of concrete block mixtures were prepared by using the low grade recycled aggregates to replace (i) natural coarse granite (10 mm), and (ii) 0, 25, 50, 75 and 100% replacement levels of crushed stone fine (crushed natural granite <5 mm) in the concrete blocks. Test results on properties such as density, compressive strength, transverse strength and drying shrinkage as well as strength reduction after exposure to 800 °C are presented below. The results show that the soil content in the recycled fine aggregate was an important factor in affecting the properties of the blocks produced and the mechanical strength deceased with increasing low grade recycled fine aggregate content. But the higher soil content in the recycled aggregates reduced the reduction of compressive strength of the blocks after exposure to high temperature due probably to the formation of a new crystalline phase. The results show that the low grade recycled aggregates obtained from the construction waste sorting facility has potential to be used as aggregates for making non-structural pre-cast concrete blocks.     

Utilization of power plant bottom ash as aggregates in fiber-reinforced cellular concrete

Recently, millions tons of bottom ash wastes from thermoelectric power plants have been disposed of in landfills and coastal areas, regardless of its recycling possibility in construction fields. Fiber-reinforced cellular concrete (FRCC) of low density and of high strength may be attainable through the addition of bottom ash due to its relatively high strength. This paper focuses on evaluating the feasibility of utilizing bottom ash of thermoelectric power plant wastes as aggregates in FRCC. The flow characteristics of cement mortar with bottom ash aggregates and the effect of aggregate type and size on concrete density and compressive strength were investigated. In addition, the effects of adding steel and polypropylene fibers for improving the strength of concrete were also investigated. The results from this study suggest that bottom ash can be applied as a construction material which may not only improve the compressive strength of FRCC significantly but also reduce problems related to bottom ash waste.     

Artificial lightweight aggregates as utilization for future ashes - A case study

In the future, more electricity in the Netherlands will be produced using coal with co-combustion. Due to this, the generated annual ash volume will increase and the chemical composition will be influenced. One of the options for utilization if present markets are saturated and for use of fly ashes with different compositions, is as raw material for lightweight aggregates. This was selected as one of the best utilizations options regarding potential ash volume to be applied, environmental aspects and status of technology. Because of this, a study has been performed to assess the potential utilization of fly ash for the production of lightweight aggregate. Lightweight aggregate has been produced in a laboratory scale rotary kiln. The raw material consisted of class F fly ash with high free lime content. An addition of 8% clay was necessary to get green pellets with sufficient green strength. The basic properties of the produced lightweight aggregate and its behaviour in concrete have been investigated. The concrete has a good compressive strength and its leaching behaviour meets the most stringent requirements of Dutch environmental regulations. The carbon foot print of concrete will be negatively influenced if only the concrete itself is taken into account, but the reduction of the volume weight has advantages regarding design, transport emissions and isolation properties which may counteract this. In the Dutch situation the operational costs are higher than expected potential selling price for the LWA, which implies that the gate fee for the fly ash is negative.     

Strength properties of concrete incorporating coal bottom ash and granulated blast furnace slag

Coal bottom ash (CBA) and fly ash (FA) are by-products of thermal power plants. Granulated blast-furnace slag (GBFS) is developed during iron production in iron and steel plants. This research was conducted to evaluate the compressive strength property and some durability characteristics of concrete incorporating FA, CBA, and GBFS. FA is used as an effective partial cement replacement; CBA and GBFS are used as partial replacement for fine aggregate without grinding. Water absorption capacity, unit weight and compressive strengths in 7, 28, and 90-day ages were assessed experimentally. For these experiments, concrete specimens were produced in the laboratory in appropriate shapes. The samples are divided into two main categories: M1, which incorporated CBA and GBFS; and M2, which incorporated FA, CBA, and GBFS. Remarkable decreases are observed in compressive strength and water absorption capacity of the concrete; bulk density of the concrete is also decreased. It can be concluded that if the content of CBA and GBFS is limited to a reasonable amount, the small decreases in strength can be accepted for low strength concrete works.     

Reuse of waste iron as a partial replacement of sand in concrete

One of the major environmental issues in Iraq is the large quantity of waste iron resulting from the industrial sector which is deposited in domestic waste and in landfills. A series of 109 experiments and 586 tests were carried out in this study to examine the feasibility of reusing this waste iron in concrete. Overall, 130 kg of waste iron were reused to partially replace sand at 10%, 15%, and 20% in a total of 1703 kg concrete mixtures. The tests performed to evaluate waste-iron concrete quality included slump, fresh density, dry density, compressive strength, and flexural strength tests: 115 cubes of concrete were molded for the compressive strength and dry density tests, and 87 prisms were cast for the flexural strength tests. This work applied 3, 7, 14, and 28 days curing ages for the concrete mixes. The results confirm that reuse of solid waste material offers an approach to solving the pollution problems that arise from an accumulation of waste in a production site; in the meantime modified properties are added to the concrete. The results show that the concrete mixes made with waste iron had higher compressive strengths and flexural strengths than the plain concrete mixes.