Recycled Aggregate Self-Curing Concrete Under Elevated Temperatures (original) (raw)
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Recycled Aggregate Self-curing High-strength Concrete
The use of recycled aggregates from demolished constructions as coarse aggregates for concrete becomes a need to reduce the negative effects on the environment. Internal curing is a technique that can be used to provide additional moisture in concrete for more effective hydration of cement to reduce the water evaporation from concrete, increase the water retention capacity of concrete compared to the conventionally cured concrete. High strength concrete as a special concrete type has a high strength with extra properties compared to conventional concrete. In this research, the combination of previous three concrete types to obtain self-curing high-strength concrete cast using coarse recycled aggregates is studied. The effect of varying water reducer admixture and curing agent dosages on both the fresh and hardened concrete properties is studied. The fresh properties are discussed in terms of slump values. The hardened concrete properties are discussed in terms of compressive, splitting tensile, flexure and bond strengths. The obtained results show that, the using of water reducer admixture enhances the main fresh and hardened properties of self-curing high-strength concrete cast using recycled aggregate. Also, using the suggested chemical curing agent increased the strength compared to conventional concrete without curing.
Curing is the name given to the procedure used for promoting the hydration of the cement and consist a control of temperature and moisture movement from the concrete. Curing allows continuous hydration of cement and consequently continuous gain in the strength, once curing stops strength gain of the concrete also stops. Proper moisture conditions are critical because the hydration of the cement virtually ceases when the relative humidity within the capillaries drops below 80%. Proper curing of concrete structures is important to meet performance and durability requirements. In conventional curing this is achieved by external curing applied after mixing, placing and finishing. Self-curing or internal curing is a technique that can be used to provide additional moisture in concrete for more effective hydration of cement and reduced self-desiccation. When concrete is exposed to the environment evaporation of water takes place and loss of moisture will reduce the initial water cement ratio which will result in the incomplete hydration of the cement and hence lowering the quality of the concrete. An experimental study carried out an investigated the use of water-soluble polyethylene glycol (PEG 6000) as self-curing agent. In this study compressive, tensile and flexural strength of self-curing concrete for 7 and 28 days and compared the use of different coarse aggregate (i.e. M35, M45 of normal coarse aggregate and recycled aggregate) and found out optimum strength.
Concrete is a building material commonly used for ages. Therefore, in the result of repairs or demolition of building structures, large amounts of concrete rubble are created, which requires appropriate management. The aim of the realized research was to determine the influence of heat and mechanical treatment of concrete rubble on the properties of recycled aggregate concrete. The research experiment included 12 series, with three variables: X 1-roasting temperature (300, 600, 900 • C), X 2-time of mechanical treatment (5, 10, 15 min), X 3-content of coarse recycled aggregates (20, 40, 60% by volume). Two additional series containing recycled aggregate without treatment and natural aggregate were also prepared. Established properties of individual aggregates have confirmed a positive effect of thermo-mechanical treatment. Then, based on the results of compressive strength, flexural strength, Young's modulus, volumetric density, water absorption, water permeability and capillarity, the most favourable parameters of heat and mechanical treatment of concrete were determined. The test results showed that appropriate treatment of concrete rubble allows to obtain high-quality coarse aggregate and valuable fine fraction. This was also confirmed by the macro-and microscopic observations of the aggregate and separated cement paste. Works realized on the concrete recycling method resulted in obtaining a patent PAT.229887.
Enhancing Early-age Properties of Self-curing Recycled Aggregate Concrete 2
2024
Recycled aggregate self-curing concrete is one of the new concrete types. It does not need to be cured using traditional curing techniques. Also, it is composed of coarse recycled aggregates rather than using traditional natural coarse aggregates to build water supply reservoirs in the concrete and continue the hydration process; some recycled aggregates can hold large amounts of water that are not included in the mixing water. This research aims to enhance self-curing recycled aggregate concrete's early-age properties. The early-age properties of recycled aggregate self-curing concrete are discussed in terms of slump values, plastic shrinkage settlement tests, and plastic shrinkage panel tests. The hardened concrete properties are noted in terms of compressive strength, splitting tensile strength, flexural strength, and bond strength (after 7, 28, and 56 days). Test results indicated that, in comparison to concrete cast using dolomite as natural aggregate, using recycled aggregate minimizes plastic shrinkage and plastic shrinkage cracks. Using polyethylene glycol (PEG400) and super absorbent polymer (SAP) as chemical curing agents also reduces plastic shrinkage and plastic shrinkage cracks in concrete
Abstract:A self-curing concrete is provided to absorb water from atmosphere to achieve better hydration of cement in concrete which solves the problem of lowered cement hydration because of improper curing and thus unsatisfactory properties of concrete. The present investigation involves the use of self-curing agent viz., polyethylene glycol (PEG) of molecular weight 6000 (PEG 6000) for dosages ranging between 0.5 to 2% by weight of cement added to mixing water. The experimental program was planned as the following. Total 120 cubes, 120 cylinders , 120 prisms were cast which involves different dosages (0%, 0.5%, 1% and 2%) of self-curing agent PEG-6000 for four different mixes (Mix 35 and Mix 45), under different curing conditions (indoor, conventional) with different aggregates (normal coarse aggregate and recycled coarse aggregate).Comparative studies were carried out for self-curing of recycled coarse aggregate and self-curing of normal coarse aggregate Comparative studies were carried out for water retentively, compressive strength, split tensile strength, flexural strength after 28 days for conventional cured and self-cured concrete. Self-curing concrete is better in all aspects compared to conventional cured concrete.
Concrete Made with Coarse Concrete Aggregate: Influence of Curing on Durability
Aci Materials Journal, 2012
Pedro Amorim is a Civil Engineer and has a Master's in Construction degree from IST, where he 8 presented his dissertation on the durability performance of concrete made with coarse recycled con-9 crete aggregates, as a function of its curing conditions. 10 Jorge de Brito MSc and PhD in civil engineering from IST. Full professor at IST and head of 11 ICIST research center. Member of IABSE, FIB, CIB and IABMAS. Research work: deterioration, 12 rehabilitation and management of concrete structures; sustainable construction. Co-author of over 13 forty-five papers in peer-reviewed journals. 14 Luís Evangelista is a member of ACI, graduated in Civil Engineering and gained his Master's from 15 IST, based on his research on the use of fine recycled concrete aggregate in concrete production. He 16 is currently continuing his research in this subject for his PhD. The author of several papers related 17 to the use of recycled aggregates in concrete production; he is a lecturer at Lisbon's Polytechnic In-18 stitute of Engineering and is also a structural designer. 19 20 ABSTRACT 21 The paper presents the main results of experiments conducted to ascertain the influence of different 22 curing conditions on the durability of recycled aggregate concrete (RAC), made with coarse crushed 23 concrete. Four different curing conditions, which represent a wide range of quality control produc-24 tion, ranging from uncontrolled outer environment conditions to standard defined temperature-25 humidity curing conditions are tested. The properties analyzed are shrinkage, water absorption by 26 2 immersion and capillarity, carbonation and chloride penetration. The general conclusion is that 27 RAC is affected by curing conditions in much the same way as CC. 28 29 30 31 Introductory remarks 32 Apart from being one of the major waste producers in the industrialized world, reaching as much as 33 45% in some cases [1], construction activities are also an important factor in the depletion of non-34 renewable, natural resources [2]. It is therefore crucial to develop technical measures to achieve sus-35 tainable industry standard procedures. This has prompted several studies on the potential of recy-36 cled and reutilized construction and demolition waste [3, 4, 5]. Today it is believed that, all things 37 being equal, concrete made exclusively with natural aggregate will perform better than concrete 38 with partial or full incorporation of recycled aggregate (RAC), the difference depending on the 39 property analyzed. However, many researchers claim that if replacement of natural aggregate with 40 recycled construction waste aggregate does not exceed 25 to 30% [6, 7] the properties of the result-41
Feasibility of Using Recycled Aggregates in Self-Curing Concrete
Recycled aggregate self-curing concrete is a new type of concrete. It can be cured without using conventional curing methods and it is made from coarse recycled aggregates instead of conventional coarse aggregates. Polyethylene Glycol is one of the chemical agents that minimize the loss of water and helps in the continuous curing of concrete. Some of the recycled aggregates can store a high amount of water that is not part of the mixing water to create water supply reservoirs in the concrete to continue the hydration process. In this investigation, the fresh and hardened properties of recycled aggregate self-curing concrete are studied. The fresh properties of recycled aggregate self-curing concrete are discussed in terms of slump values. The hardened concrete properties of recycled aggregate self-curing concrete are discussed in terms of the compressive strength at 7 and 28 days. Also, the tensile splitting strength, flexural strength, and the bond strength at 28 days are studied. It was found that using superplasticizer SP enhances the main fresh and hardened concrete properties of recycled aggregate concrete, also using Polyethylene glycol as a chemical curing agent increases the strength of recycled aggregate self-curing compared to conventional cured concrete.
IOP Conference Series: Earth and Environmental Science, 2018
Concrete is the chief material of construction and it is non-combustible in nature. However, the exposure to the high temperature such as fire can lead to change in the concrete properties. Due to the higher temperature, several changes in terms of mechanical properties were observed in concrete such as compressive strength, modulus of elasticity, tensile strength and durability of concrete will decrease significantly at high temperature. The exceptional fireproof achievement of concrete is might be due to the constituent materials of concrete such as its aggregates. The extensive use of aggregate in concrete will leads to depletion of natural resources. Hence, the use of waste and other recycled and by-product material as aggregates replacements becomes a leading research. This review has been made on the utilization of waste materials in concrete and critically evaluates its effects on the concrete performances during the fire exposure. Therefore, the objective of this paper is to review the previous search work regarding the concrete containing waste material as aggregates replacement when exposed to elevated temperature and come up with different design recommendations to improve the fire resistance of structures.
Effects of using recycled concrete as aggregate on the engineering properties of concrete
National Seminar on the use of recycled materials in engineering construction, 1996
Waste concrete produced from demolition of concrete structures is an alternative source for the production of concrete aggregates and acceptance of recycled concrete aggregates for the production of new concrete depends on the quality of them. This paper discusses results of a series of investigations into the properties of recycled concrete aggregates and the effects of using them on the properties of concrete. Concrete aggregates differ from the natural aggregates due to the presence of a considerable proportion of mortar attached to the natural aggregates and consequently affecting the properties and performance of concrete. The results st..ow that for recycled aggregate concrete, compressive and tensile strengths and modulus are reduced, whereas drying shrinkge and creep are increased. The effect of using concrete fine aggregate on the modulus and shrinkage is less than those produced by the use of concrete coarse aggregate. The strength of recycled aggregate concrete can be recovered by making suitable mix adjustments or by the addition of fly ash or silica fume. Modulus of elasticity, drying shrinkage and creep cannot be fully recovered, by the above methods although improvements were observed.