Efeito da pré-molhagem do agregado nas propriedades das argamassas com agregado reciclado deconcreto e agregado leve

This paper examines the suitability of partially replacing natural aggregate, sand, (NA) with recycled concrete aggregate (RCA) or lightweight aggregate (LWA) in mortars, under the hypothesis that pre-wetting aggregates would produce improvement in mortar properties. Fresh mortar properties such as density, entrained air content, consistency and heat of hydration, as well as hardened mortar properties such as dry density, compressive and flexural strength, and dimensional instability at 0% and 100% saturation were determined. The results show that mortars made with natural aggregate (75%) and recycled concrete aggregate (25%) have similar properties to mortars made with only natural aggregate (100%) and that pre-wetting the aggregates does not influence the properties of mortars significantly. Therefore, partial replacement with recycled concrete aggregate is a viable alternative for producing mortar.Peer ReviewedPostprint (published version

Study for re-ASR behaviour of recycled concrete using ASR generated concrete and considering countermeasure technology

It is predicted that the concrete volume to be discarded will increase due to the renewal of the concrete structures and the increase in the returned concrete from construction site. The use of this concrete block as recycled aggregate is very important in terms of sustainability. However, recycled aggregate concrete is difficult to use due to large problems such as drying shrinkage and freeze-thaw action. On the other hand, the aggregate used for the raw concrete is often unknown, suggesting the danger of ASR. There is no previous research about what kind of danger is caused when an aggregate having an ASR risk is used as a recycled aggregate. Therefore, in this study, recycled aggregate was made from raw concrete where ASR occurred, after that recycled concrete was manufactured using this aggregate. After this, ASR tests were conducted again for the recycled concrete. In addition, we examined whether recycled concrete using aggregates with properties improved by using the previously reported carbonation technique could be an ASR countermeasure technology. As a result, it was found that the recycled concrete using the ASR-generated raw concrete as aggregate can suppress ASR by using recurring ASR aggregate treated by carbonation technology

Performance Evaluation Analyses of Recycled Concrete in Albania by using Ultrasonic Pulse Velocity

This paper is focused on investigation of the possibility of using recycled aggregate in concrete mixes instead of natural aggregate. Our research included the preparation of concrete mixtures with recycled aggregate of concrete and natural fine aggregate. It has been focused on evaluation of compressive strength of old and new concrete, granulometric distribution analysis of recycled concrete, density of new and old concrete, water permeability in concrete, and measuring of Ultrasonic Pulse Velocity (UPV) for our samples. According to experimental results, the use of recycled aggregate in concrete mixes as an alternative to natural aggregate is possible. The experimental results demonstrate that recycled aggregates of concrete can achieve higher durability

Waste Concrete as a Source of Aggregate for New Concrete

Three concrete mixes of widely differing water cement ratios were made using crushed waste concrete as coarse aggregate. The properties investigated include the physical properties of the recycled aggregate, the compressive and flexural strengths of the concrete. These properties were compared with those of similar concrete specimens made with conventional natural aggregate. Also tested was the compressive strength of concrete cubes cut from the waste concrete. Results of the tests suggest that the strength of concrete made from recycled waste concrete aggregate is dependent on the strength of the original concrete from which the recycled aggregate is derived. It is concluded that recycled aggregate can be used to produce quality concrete when the strength of concrete required is not greater than the strength of the original concrete from which the recycled aggregate is derived

Macro- and micro- properties of multi-recycled aggregate concrete

ABSTRACT: In a future scenario in which all the concrete is recycled concrete, it will be necessary to recycle the recycled concrete. However, it is known that the recycling of concrete implies a loss of properties. This paper shows an innovative technique, the computerized microtomograph, used to evaluate closed porosity, volume of limestone aggregate fraction and volume of mortar of the multi-recycled aggregate concrete, in order to answer the question: how many times it is possible to recycle concrete? First, the source concrete mix using limestone coarse and fine aggregates was characterized. This mix was crushed to obtain a recycled aggregate that was used to manufacture the 1st generation or current recycled aggregate concrete. After the characterization of this 1st generation concrete, and in the same way, a 2nd and a 3rd generation concrete were obtained and characterized, using recycled aggregates from the 1st and 2nd concrete generations respectively. The evaluation by computerized axial tomography allows to know how the successive recycled affect the properties of the concrete. The results show that it is possible to observe the distribution and quantify the aggregate, cement paste and closed porosity contents of the recycled aggregate concrete showing that 3rd generation recycled concrete shows almost twice as much mortar as 1st generation one and demonstrates that it is only possible to recycle the concrete a finite number of times

Stress-strain characteristics and energy absorption analysis of Construction and demolition waste recycled aggregate concrete in compression

The stress strain characteristics and mechanical properties of construction and demolition aggregate concrete at two different w/c ratios – 0.4 and 0.5 are presented in this study. The mechanical and stress strain characteristics of recycled aggregate concrete are compared to the properties and Stress strain characteristics of the conventional aggregate concrete. The mechanical properties include the cube and cylindrical compressive strength, Modulus of elasticity, flexural strength, split tensile strength and hardened density. Under stress strain characteristics, strain at peak stress and the energy absorbed under compression is included. The study aimed to correlate and compare the behaviour of recycled aggregate concrete and Conventional aggregate concrete having comparable strength. Finally, the experimental stress strain characteristics of the Recycled aggregate concrete is analysed for its compatibility of the assumed stress strain behaviour of concrete in IS 456. According to the findings, recycled aggregate concrete has similar stress-strain characteristics to conventional aggregate concrete of comparable strength, and existing stress block parameters can be suitably used for the recycled aggregate concrete

Prediction of compressive strength of general-use concrete mixes with recycled concrete aggregate

This paper presents the mechanical behaviour of concrete mixes made with recycled aggregate by replacing the natural aggregate with crushed concrete from pavement demolition. The purpose of this study was to determine the feasibility of using recycled aggregate from pavement demolition to make new concrete for pavement applications. Considering a control mix without recycled aggregate (RCA0) designed for a compressive strength of 34 MPa, two types of concrete mixes with 50% (RCA50) and 100% (RCA100) replacement percentage of natural coarse aggregate by recycled aggregate were made. The resulting concrete specimens were tested at three different curing ages, 7, 14, and 28 days. The results of this study showed that the compressive and flexural strengths decreased for all two mixes as the recycled aggregate content increased, while the density was slightly affected. A new model based on multiple linear regression analysis of the data from this study and other 14 studies from the literature was developed. The model can be used to predict the compressive strength of general-use concrete mixes with recycled aggregate (20–40 MPa) considering both the recycled aggregate content and the curing age of concrete. A good correlation was found between the compressive strength and the two parameters investigated. Given the predictions of this model, it is recommended not to use more than 30% recycled concrete aggregate in the production of new concrete in order not to affect its strength

Engineering properties of porous concrete made of sustainable aggregate

The effect of using different types of aggregate on engineering properties of previous concrete is experimentally evaluated in this study. For this purpose, a total of four concrete mixes are cast and tested. The main parameters studied in this study are the aggregate type (natural and recycled) and aggregate size. The recycled aggregate was provided from damaged pavement roads at Amarah city. The flexural and compressive strength, infiltration, and permeability of pervious concrete are recorded throughout the study. The results of study revealed that the mechanical and physical properties of previous concrete made of recycled aggregate confirms with the international specifications. Furthermore, the conclusions appear the ability of using recycled aggregate from damaged road pavements as aggregate for producing the pervious concrete have an acceptable engineering properties. The utilizing of recycled aggregate contributes to reduce the pollution and represent as a kind of sustainability of this type of concrete materials

Concrete manufacture with un-graded recycled aggregates

Purpose – The purpose of this paper is to investigate whether concrete that includes un-graded recycled aggregates can be manufactured to a comparable strength to concrete manufactured from virgin aggregates. Design/methodology/approach – A paired comparison test was used to evaluate the difference between concrete made with virgin aggregates (plain control) and concrete including recycled waste. Un-graded construction demolition waste and un-graded ground glass were used as aggregate replacements. With regard to concrete, compressive strength is widely used as a measure of suitability as being fit for purpose. Therefore compressive strength was mainly used to compare the different concrete batches; however density was measured across the range of samples. Findings – The findings show that a lower average compressive strength is achieved when compared to the plain control sample manufactured with virgin aggregates. Correct particle packing may not be achieved and grading of aggregates is essential prior to mix design. The recycled aggregate was highly variable in terms of the fine particle content, which affected the water demand of the concrete. Practical implications – This manufacturing practice is considered necessary because of the current trend in using waste products in concrete to replace binders and aggregates; thus reducing the impact on the environment and use of finite natural resources. The research shows the risk of mixing concrete using a simple aggregate replacement without careful aggregate grading and adjustments to the mix design. Originality/value – The paper examines 100 per cent ungraded aggregate replacement with glass and demolition waste

A two-step approach for calculating chloride diffusion coefficient in concrete with both natural and recycled concrete aggregates.

This paper presents an analytical approach to calculate the effective diffusion coefficient of chlorides in concrete with both natural and recycled concrete aggregates. In the approach the concrete is treated as a composite consisting of three phases, namely mortar, natural aggregate plus interfacial transition zone, and recycled concrete aggregate plus interfacial transition zone. The effective diffusion coefficient of chlorides in the composite is calculated through two steps. The first step is to calculate the effective diffusion coefficients of chlorides in the natural aggregate plus interfacial transition zone and in the recycled concrete aggregate plus interfacial transition zone by using multilayer spherical approximation, the results of which provide the information about the quality of recycled concrete aggregate in terms of chloride penetration resistance. The second step is to calculate the effective diffusion coefficient of chlorides in the three-phase concrete composite by using effective medium approximation, the results of which provide the information about the influence of recycled concrete aggregate on the diffusivity of recycled aggregate concrete. The analytical expression of the effective diffusion coefficient is derived and carefully compared with the results obtained from both the experiments and numerical simulations, which demonstrates that the present analytical model is rational and reliable. The analytical expression presented can be used to predict the service life of recycled aggregate concrete exposed to chloride environment