Papers by Keyword: Recycled Aggregate

Abstract: The utilisation of concrete has significant environmental repercussions, including CO2 emissions (notably from cement production), the exhaustion of natural resources due to aggregate extraction, and the disposal of debris in landfills. In concrete production, recycled aggregate has a minimal direct effect on greenhouse gas emissions, as the predominant source of emissions is cement production. Its contribution is in diminishing the extraction of raw materials required for concrete production, hence decreasing waste and safeguarding natural resources. This paper examines the resistance of small columns constructed from concrete with recycled material. The essay outlines the results of experimental assessments of eccentrically loaded columns. The modulus of elasticity of concrete, including recycled aggregate, particularly when incorporating masonry and mixed material, markedly diminishes in comparison to concrete composed of natural aggregate or recycled concrete aggregate. Currently, recycled masonry or mixed aggregate is predominantly used in embankments, sub-base layers of roadways, and non-load-bearing structural components. To present, experiments have predominantly concentrated on its application in concrete components exposed to bending and shear forces. The utilisation of recycled masonry aggregate may have substantial applications in large piers, where the impact of a reduced modulus of elasticity would be minimal due to the primarily compressive load. In the experiment, following the normalisation of strengths, the samples exhibited comparable resistance; the sample with a 50% proportion of RA demonstrated nearly identical resistance to the reference column (0% RA proportion). The sample with a complete 100% share of RA exhibited a 6.57% increase in normalised resistance relative to the reference column.

Abstract: Growing concerns about sustainability and the search for greener alternatives in construction have led to a renewed interest in recycled concrete as a building material. Recycled concrete is produced using recycled aggregates, such as construction and demolition debris, instead of virgin aggregates, which reduces the demand for natural resources and the accumulation of waste. However, the viability of recycled concrete in high-temperature applications, such as fires or exposure to extremely high temperatures, has come under critical scrutiny. In this study we are going to talk about the differences between conventional concrete and concrete with recycled aggregate after being exposed to high temperatures, we will focus on issues of resistance to compression, traction and modulus of elasticity. We were able to obtain in our tests that the greater the amount of recycled aggregate that we use in the concrete, the lower mechanical properties we obtain with respect to conventional concrete after being exposed to high temperatures, this is due to the adhered mortar that the recycled aggregate presents (in in our case 42% adhered mortar).

Abstract: The circular economy is currently a highly discussed topic in many areas of production, due to the potential scarcity of natural resources. In the construction sector, it is often associated in the first place with the high shortages of natural aggregates for the production of concrete. To produce concretes up to strength classes C 30/37, the partial or complete replacement of natural aggregates by concrete or brick crushed recyclates in the 4/22 mm fraction can be used very efficiently and safely. This paper will show the current legislative limitations for the use of recyclates as aggregates for concrete production, the possibilities of their use when limiting the degrees of environmental influence or physico-mechanical parameters. In both cases of strength classes C 16/10 and C 30/37, a decrease in compressive strength of 16% was observed with replacement of coarse natural aggregate. The results of physico-mechanical properties of different formulations experimentally and practically verified will be shown and the areas of their safe use will be discussed.

Abstract: River sand, one of the ingredients for concrete when harvested uncontrollably from the river would cause destruction to the river environment. At the same time, the increasing concrete waste disposed at dumpsite after generated from construction and demolition activity causes environmental pollution. The approach of recycling concrete waste for use as a mixing component in concrete production would lessen the heavy reliance on natural sand supplies and lower the amount of concrete waste disposed. The current study investigates the effect of recycled fine aggregate obtained from concrete waste as sand replacement on concrete's workability, compressive strength, and water absorption. Five mixtures were made using varying amounts of recycled fine aggregate (0, 10, 20, 30 and 40% by weight of sand). All specimens were subjected to water curing. Three types test were conducted namely slump test, compressive strength test and water absorption test. Findings show that the integration of recycled fine aggregate up to 20% produces concrete with the targeted strength of 40MPa. Furthermore, the water absorption of the mixes is less than 3%, allowing it to be classified as good quality. Success in blending recycled fine aggregate in concrete production would contribute to saving river sand consumption and lesser concrete waste for a cleaner environment.

Abstract: The present contribution reports the results of the experimental investigation on a sustainable lightweight cementitious composite material, in which virgin sand is partially substituted by a very fine composite powder retrieved from the manufacturing process of kitchen and sanitary ware. In order to obtain lightweight structural concrete suitable for screeds, the mixture is completed by the addition of recycled polyethylene terephthalate aggregates and lightweight glass spherules. First, physical and morphological properties of the raw powder are thoroughly investigated. Then, the mechanical response of the composite is assessed by means of three-point bending tests and uni-axial compression tests. The conglomerates exhibit promising mechanical performance, thus being regarded as possible candidate for innovative and sustainable structural applications.

Abstract: Air lime coating mortars with mussel shells exhibit useful hygrothermal properties related to humidity and temperature regulation. Introducing mussel shell sand produces a significant increase in pore volume, changing mortar’s microstructure and reducing density. This is attributed to the flaky and irregular shape of the shell particles that present also traces of organic matter. In this work, the natural aggregate is replaced by mussel shell sand in increasing percentages of 25%, 50% and 75%. Additionally, a mortar with 0% of sand replacement is used as baseline of reference. These mortars are tested focusing in two main parameters, in first term, thermal conductivity. And also absorption and desorption cycles, at 80 and 50% relative humidity. The results are very positive for mussel shells specimens, it can be concluded that the use of mussel shell aggregates can improve the hygrothermal properties of air lime coating mortars. Another interesting result is a subjective property such as the aesthetic quality of the finishing, the results is pleasing and, combined with the promising hygrothermal properties opens a good opportunity for mussel shell mortars.

Abstract: Concrete containing recycled aggregates have different properties from concrete containing natural aggregates. This work investigates, firstly, the possibility of using recycled refractory bricks (RBA) as coarse aggregate for concrete, and secondly, finds the ideal replacement percentage of natural coarse aggregate (NCA) by RBA. For this, an experimental study was carried out to assess the physical and mechanical properties of concrete produced with the partial and total replacement of NCA by RBA. Two types of RBA from two different sources were used, RBA-1 obtained from the grinding of new refractory bricks and RBA-2 obtained from refractory bricks used in the furnace recovered from the cement plant. For each type of RBA, two concretes with water/cement (w/c) ratios of 0.59 and 0.38 were tested. These concretes were evaluated by density, water porosity, ultrasonic pulse velocity (UPV) and compressive strength, and compared to those obtained on conventional concretes. The results obtained show that concrete can be manufactured using RBA. Concrete containing 20% ​​RBA shows good quality compared with conventional concrete.

Abstract: To develop a sustainable concrete and to minimize the depletion of the natural resources, an attempt was made to develop sustainable concrete mixtures benefiting from the geopolymer technology and the use of recycled aggregate in self-compacting geopolymer concrete (SCGC). This study aim to examine the effects of sodium hydroxide (SH) molarity and sodium silicate (Na2SiO3)/ sodium hydroxide (SS/SH) ration the fresh properties of SCGC mixtures containing recycled coarse aggregates (RCA) Mixes were prepared with three different molarity (8M, 10M and 12M) of) and four SS/SH ratios (1.5, 2.0, 2.5 and 3.0). Six mixes were examined in this study. The results were compared with the EFNARC limits for self-compacting concrete (SCC). It was found that the SS/SH ratio and the molarity of SH affect the fresh properties of (SCGC). However, the results showed that, SCGC mixtures containing RCA can be developed and satisfy the requirements of EFNARC for fresh state of SCC.

Abstract: Alkali activated slag (AAS) has gained huge attention in recent years due to its ability to replace ordinary Portland cement (OPC) as a binder in concrete. A need to replace OPC is imminent due to the high carbon dioxide emitted into the environment during its production. However, the use of this type of binder did not eliminate the huge strain placed on the deposit of natural resources. With the demand for concrete predicted to rise significantly in coming years, this means there will be a consequential increase in the amount of natural deposits of aggregates exploited, as aggregates make up about 80% by the volume of concrete. Therefore, in order to meet this forthcoming demand of sustainable concrete, and reduce the excessive strain on the use of natural aggregates, it is essential to find alternative materials that can be used as aggregate in concrete using AAS as a binder. This paper summarizes experimental results from various studies on the use of waste materials on aggregate. The fresh and hardened properties, alongside the cost and sustainability indications, are explored. It was drawn from this review that more reduction in carbon dioxide emission and cost could be achieved with the use of waste materials as aggregate in concrete. In addition, concrete made with AAS as a binder and incorporating waste as aggregate showed similar/higher properties with those made with natural aggregate. However, proper selection of types of wastes and replacement levels of these waste materials used as aggregate is still required to achieve enhanced properties.

Abstract: Green concrete is a recent sustainable practice in UAE that was enforced by Dubai Municipality in construction field within the emirate of Dubai to reduce the carbon foot print in construction industry and to increase the durability of the structures. This led the construction industry to reduce the usage of ordinary portland cement by replacing it with supplementary cementitious materials (SCMs) such as Grand Granulated Blast Furnace Slag (GGBS) and flyash (FA). Incorporating GGBS or FA in concrete mixtures can improve durability parameters of hardened concrete, such as resistance to water permeability, reduced water absorption and chloride penetration. This ultimately increases the structure’s service life by increasing the threshold of concrete mixture for chloride induced corrosion. On the other hand, carbonation induced corrosion to concrete is usually being ignored or forgotten generally, due its usual slow rate ingression in plain portland cement concrete mixtures. Several studies showed that incorporating some types of SCM – especially at high percentage - can reduce the concrete resistance to carbonation. Additionally and for concrete with recycled aggregate, carbonation investigation should be taken into consideration. This is since recycled aggregates are reused aggregates that are extracted from demolished structures and buildings which were already subjected to different environmental exposures and deteriorations. Unlike chloride penetration, there is no direct ASTM standard test to anticipate the concrete mixture resistance to carbonation at early ages. In this study, concrete mixtures with flyash and different recycled aggregate replacement percentages are investigated for carbonation resistance in accelerated proposed method, considering concrete mixtures’ key parameters like water-cement ratio, and total cement content. The results are analyzed to arrive to pertinent conclusions for the best utilization of sustainable concrete for carbonation resistance.