Effects of Concrete Grades on Strength Characteristics of Metakaolin Modified Recycled Aggregate Concrete

In this study, locally produced Metakaolin (MK) was used as an admixture in recycled aggregate concrete of grades M 25 and M 30. The content of MK varied from 0-15% at 5% intervals. The physical and mechanical properties (bulk density, specific gravity, water absorption, aggregate crushing value and aggregate impact value) of aggregates were determined, the chemical composition as well as reactivity of MK was evaluated using X-Ray Fluorescence (XRF) technique and modified Chappelle test. The workability (slump) and strength (compressive and split tensile) properties of fresh and hardened RAC were examined relative to that of conventional concrete. The results of the experiments revealed that the specific gravity (SG), water absorption and aggregate impact value of recycled aggregates (RA) were 2.23, 5.35% and 32%, respectively. The MK used had an optimum reactivity of 2060.8 mg of Ca(OH)2 fixed at a temperature of 660 oC. The slump values for M 25 and M 30 control specimens were 72 mm and 65 mm, respectively while the slump values of MK modified RAC decreased from 67-45 mm for M 25 and 55-35 mm for M 30 as MK increased from 0-15%. The 56th-day compressive strength of the control samples was 21.73 N/mm2 for M 25 and 26.8 N/mm2 for M 30, respectively, while RAC samples ranged from 14.96 - 17.04 N/mm2 for M 25 and 20.55 - 22.67 N/mm2 for M 30 whereas the split tensile strength for the control samples was 2.71 N/mm2 and 3.06 N/mm2 for the two grades in that sequence, while those of RAC ranged from 2.26-2.49 N/mm2 for M 25 and 2.62 – 2.84 N/mm2 for M 30. Despite the fact that metakaolin modified RAC had lower strength properties than conventional concrete, the use of 10% metakaolin as a RA modifier in concrete production will provide a sustainable alternative to conventional aggregates in concrete mix design.

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Using Neural Networks to Determine the Significance of Aggregate Characteristics Affecting the Mechanical Properties of Recycled Aggregate Concrete

Applied Sciences ◽

10.3390/app8112171 ◽

2018 ◽

Vol 8 (11) ◽

pp. 2171 ◽

Cited By ~ 6

Author(s):

Zhenhua Duan ◽

Shaodan Hou ◽

Chi-Sun Poon ◽

Jianzhuang Xiao ◽

Yun Liu

Keyword(s):

Neural Networks ◽

Compressive Strength ◽

Elastic Modulus ◽

Specific Gravity ◽

Water Absorption ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Aggregate Concrete ◽

Curing Age

It has been proved that artificial neural networks (ANN) can be used to predict the compressive strength and elastic modulus of recycled aggregate concrete (RAC) made with recycled aggregates from different sources. This paper is a further study of the use of ANN to analyze the significance of each aggregate characteristic and determine the best combinations of factors that would affect the compressive strength and elastic modulus of RAC. The experiments were carried out with 46 mixes with several types of recycled aggregates. The experimental results were used to build ANN models for compressive strength and elastic modulus, respectively. Different combinations of factors were selected as input variables until the minimum error was reached. The results show that water absorption has the most important effect on aggregate characteristics, further affecting the compressive strength of RAC, and that combined factors including concrete mixes, curing age, specific gravity, water absorption and impurity content can reduce the prediction error of ANN to 5.43%. Moreover, for elastic modulus, water absorption and specific gravity are the most influential, and the network error with a combination of mixes, curing age, specific gravity and water absorption is only 3.89%.

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Durability Studies on the Recycled Aggregate Concrete in China over the Past Decade: A Review

Advances in Civil Engineering ◽

10.1155/2019/4073130 ◽

2019 ◽

Vol 2019 ◽

pp. 1-19 ◽

Cited By ~ 6

Author(s):

Zhiming Ma ◽

Qin Tang ◽

Dingyi Yang ◽

Guangzhong Ba

Keyword(s):

Water Absorption ◽

Absorption Rate ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Rapid Urbanization ◽

Aggregate Concrete ◽

The Past ◽

Water Absorption Rate ◽

Average Water

Since China hosted the Olympic Games in 2008, a mass of construction and demolition (C&D) wastes were produced with the rapid urbanization construction. Recycling the C&D waste into recycled aggregates (RA) is an effective method for reducing the amount of C&D wastes. Many studies on the properties of RA and the durability of recycled aggregate concrete (RAC) were conducted in China over the past decade. Due to the restrictions of various languages, some valuable studies on the durability of RAC are hard to be acquired by the scholars around the world. Therefore, this paper is developed to review the studies on the durability of RAC in China, and the shrinkage behavior, chloride permeability, carbonation behavior, and freeze-thaw resistance of RAC are, respectively, introduced. Considering the waste concrete, bricks, and ceramics used in preparing RA are frequently mixed together in China, this study proposes an index of average water absorption rate to quantify the effects of RA types, quality, and replacement percentages on the durability of RAC. Meanwhile, the relationship between the average water absorption rate of RA and the durability parameters of RAC is established. Finally, the improving methods of RAC durability are introduced, and the RA particle shaping and carbonation modification are emphasized.

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A Study Based upon the Usage Recycled Aggregate to Enhance the Strength Aspects of Conventional Concrete: A Critical Review

International Journal for Research in Applied Science and Engineering Technology ◽

10.22214/ijraset.2021.35222 ◽

2021 ◽

Vol 9 (VI) ◽

pp. 1567-1570

Author(s):

Suhail Mushtaq Khan

Keyword(s):

Chloride Ions ◽

Recycled Concrete ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Concrete Aggregate ◽

Split Tensile Strength ◽

Conventional Concrete ◽

Natural Aggregate ◽

Concrete Production

Recycled aggregates are those crushed cement concrete or asphalt pavement which comes out from the construction debris which is reused in construction. They are made from the reprocessing of materials which have been used in previous constructions. This paper discusses about the study of properties of recycled aggregates from the sources which has already been published. The results are that 100% replacement of natural aggregate by recycled concrete aggregate effect on chloride ions resistance, it plays negative effects on durability of recycled concrete aggregates, and addition of fiber in recycled aggregate concrete mixture gave more effective in the performance of concrete. On experimental study of recycled aggregate, compressive, flexural and split tensile strength of the recycled aggregate were found to be lower than that of the natural aggregate. Use of recycled aggregate in a new concrete production is still limited. Recommendation of introduction of recycled aggregates standard is required for the materials to be used successfully in future. Gaps in literature reviews are also included in this paper.

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Geopolymer Recycled Aggregate Concrete: From Experiments to Empirical Models

Materials ◽

10.3390/ma14051180 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1180

Author(s):

Hoai-Bao Le ◽

Quoc-Bao Bui ◽

Luping Tang

Keyword(s):

Sodium Hydroxide Solution ◽

Empirical Models ◽

Recycled Aggregate Concrete ◽

Curing Temperature ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Fine Aggregate ◽

River Sand ◽

Conventional Concrete ◽

Aggregate Concrete

Ordinary cement concrete is a popular material with numerous advantages when compared to other construction materials; however, ordinary concrete is also criticized from the public point of view due to the CO2 emission (during the cement manufacture) and the consumption of natural resources (for the aggregates). In the context of sustainable development and circular economy, the recycling of materials and the use of alternative binders which have less environmental impacts than cement are challenges for the construction sector. This paper presents a study on non-conventional concrete using recycled aggregates and alkali-activated binder. The specimens were prepared from low calcium fly ash (FA, an industrial by-product), sodium silicate solution, sodium hydroxide solution, fine aggregate from river sand, and recycled coarse aggregate. First, influences of different factors were investigated: the ratio between alkaline activated solution (AAS) and FA, and the curing temperature and the lignosulfonate superplasticizer. The interfacial transition zone of geopolymer recycled aggregate concrete (GRAC) was evaluated by microscopic analyses. Then, two empirical models, which are the modified versions of Feret’s and De Larrard’s models, respectively, for cement concretes, were investigated for the prediction of GRAC compressive strength; the parameters of these models were identified. The results showed the positive behaviour of GRAC investigated and the relevancy of the models proposed.

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Elasto-Damage Constitutive Modelling of Recycled Aggregate Concrete

International Journal of Materials ◽

10.46300/91018.2020.7.16 ◽

2020 ◽

Vol 7 ◽

Keyword(s):

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Percentage Increase ◽

Test Results ◽

Conventional Concrete ◽

Critical Energy Release Rate ◽

Aggregate Concrete ◽

Finite Element Software ◽

Concrete Model

Use of recycled aggregates in concrete has proved to be beneficial in attaining sustainable construction without compromising overall material and structural performance when compared with concrete containing natural aggregates. However, use of the recycled aggregates in concrete have resulted in reduction in compressive and tensile strengths with the recycled aggregates percentage increase in concrete. Furthermore, it is important to note that most of the finite element software used in the construction industry use concrete model derived from the test results of the conventional concrete, therefore, they may not always predict safe solution for recycled aggregates concrete (RAC). Therefore, in this investigation elasto-damage, proposed by Khan and Zahra, for natural aggregate concrete (NAC) was modified to incorporate the influence of recycled aggregates on the behaviour of concrete. Model use four parameters α, β, γ critical energy release rate (Rc) to predict the behaviour of recycled aggregate concrete for multi axial stress states. Parameters α, β and γ are used to predict the different behavior of concrete in tension and compression while Rc controls the damage growth rate. These parameters are defined as a function of concrete compressive strength (fc/) and its initial elastic modulus (Eo). Existing test results for uniaxial compressive state of stress were used to validate this model and it was found that it predicts better post cracking and post peak-behaviour of RAC as compared to the commercially available models for conventional concrete

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Confinement Effect and Efficiency of Concentrically Loaded RACFCST Stub Columns

Materials ◽

10.3390/ma15010154 ◽

2021 ◽

Vol 15 (1) ◽

pp. 154

Author(s):

En Wang ◽

Yicen Liu ◽

Fei Lyu ◽

Faxing Ding ◽

Yunlong Xu

Keyword(s):

Bearing Capacity ◽

Ultimate Bearing Capacity ◽

Recycled Aggregate Concrete ◽

Confinement Effect ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Replacement Ratio ◽

Conventional Concrete ◽

Aggregate Concrete ◽

Stub Columns

Recycled aggregate concrete-filled steel tubular (RACFST) columns are widely recognized as efficient structural members that can reduce the environmental impact of the building industry and improve the mechanical behavior of recycled aggregate concrete (RAC). The objective of this study is to investigate the behavior of recycled aggregate concrete-filled circular steel tubular (RACFCST) stub columns subjected to the axial loading. Three-dimensional finite element (FE) models were established using a triaxial plastic-damage constitutive model of RAC considering the replacement ratio of recycled aggregates. The FE analytical results revealed that the decreased ultimate bearing capacity of RACFCST stub columns compared with conventional concrete infilled steel tubular (CFST) columns was mainly due to the weakened confinement effect and efficiency. This trend will become more apparent with the larger replacement ratio of recycled aggregates. A practical design formula of the ultimate bearing capacity of RACFCST stub columns subjected to axial load was proposed on the basis of the reasonably simplified cross-sectional stress nephogram at the ultimate state. The derivation process incorporated the equilibrium condition and the superposition theory. The proposed equation was evaluated by comparing its accuracy and accessibility to some well-known design formulae proposed by other researchers and some widely used design codes.

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Evaluating the durability of recycled concrete made of coarse recycled aggregate concrete containing silica-fume and natural zeolite

10.7764/rdlc.19.3.457-473 ◽

2020 ◽

Vol 19 (3) ◽

pp. 457-473

Author(s):

Hasan Jalilifar ◽

◽

Fathollah Sajedi ◽

Vahid Razavi Toosi ◽

◽

...

Keyword(s):

Water Absorption ◽

Silica Fume ◽

Natural Zeolite ◽

Full Scale ◽

Recycled Concrete ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Conventional Concrete ◽

Aggregate Concrete ◽

Four Levels

This experimental study evaluates the durability of recycled aggregate concrete (RAC) containing silica-fume (SF) and natural zeolite (NZ). For this purpose, four levels of recycled coarse concrete aggregates (RCA) were replaced with natural coarse aggregates (NCA). To compare the effect of pozzolans, three levels of SF (5%, 10%, and 15%) and three levels of NZ (10%, 20%, and 30%) were replaced with cement. To evaluate the durability of RAC, 28 mixed designs were made and the following were measured: compressive strength (CS), water absorption by immersion (WA by immersion), water absorption by capillary (WA by capillary), electrical resistance (ER), electrical conductivity (EC) and rapid chloride penetration test (RCPT). The results indicated that WA by immersion and WA by capillary of RAC increased with enhanced RCA incorporation. On the other hand, the pozzolanic reaction of 10% of SF and 10% of NZ decreased capillary pores and structural weakness of full-scale RAC. However, due to the internal chemical changes of RAC, contrary to the WA by immersion and WA by capillary, compared to conventional concrete (CC), a lower EC and unchanged ER values of RC100 containing pozzolans were seen. The scanning electron microscopy (SEM) revealed that compared to NZ, a 10% of SF significantly improved the microstructure of full scale RAC.

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Virtual Revision on Compressive Srength of Conventional Concrete and Recycled Aggregate Concrete Consisting Treated Recycled Aggregate

International Journal of Recent Technology and Engineering - 2 ◽

10.35940/ijrte.c5067.098319 ◽

2019 ◽

Vol 8 (3) ◽

pp. 3439-3443

Keyword(s):

Experimental Studies ◽

Strength Properties ◽

Recycled Concrete ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Concrete Aggregate ◽

Conventional Concrete ◽

Aggregate Concrete ◽

Natural Aggregate

Use of reused aggregate in concrete can be useful for the ecological protection and economical terms. The application of recycled has been started in many construction projects. Paper hear says the basic properties of recycled concrete aggregate. It similarly relates the properties with natural aggregate, similarly the properties of recycled aggregates concrete were also determined and explained here. For the concrete grades of M25 and M30, the recycled aggregate concrete is produced by changing the natural aggregate, by recycled aggregate in conventional concrete with 5%, 10% and 15% of weight of natural aggregates. Experimental studies were carried out on influence of recycled aggregate treatment and comparison of strength properties of conventional cement concrete and recycled aggregate concrete at the curing of 7days and 28 days. They are two types of treatments under the considerations for recycled aggregates are Abrasion of recycled aggregate and chemical immersion

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Recycled Aggregates Concrete Compressive Strength Prediction Using Artificial Neural Networks (ANNs)

Infrastructures ◽

10.3390/infrastructures6020017 ◽

2021 ◽

Vol 6 (2) ◽

pp. 17

Author(s):

Mohamad Ali Ridho B K A ◽

Chayut Ngamkhanong ◽

Yubin Wu ◽

Sakdirat Kaewunruen

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Strength Prediction ◽

Concrete Compressive Strength ◽

Conventional Concrete ◽

Aggregate Concrete ◽

Ann Models

The recycled aggregate is an alternative with great potential to replace the conventional concrete alongside with other benefits such as minimising the usage of natural resources in exploitation to produce new conventional concrete. Eventually, this will lead to reducing the construction waste, carbon footprints and energy consumption. This paper aims to study the recycled aggregate concrete compressive strength using Artificial Neural Network (ANN) which has been proven to be a powerful tool for use in predicting the mechanical properties of concrete. Three different ANN models where 1 hidden layer with 50 number of neurons, 2 hidden layers with (50 10) number of neurons and 2 hidden layers (modified activation function) with (60 3) number of neurons are constructed with the aid of Levenberg-Marquardt (LM) algorithm, trained and tested using 1030 datasets collected from related literature. The 8 input parameters such as cement, blast furnace slag, fly ash, water, superplasticizer, coarse aggregate, fine aggregate, and age are used in training the ANN models. The number of hidden layers, number of neurons and type of algorithm affect the prediction accuracy. The predicted recycled aggregates compressive strength shows the compositions of the admixtures such as binders, water–cement ratio and blast furnace–fly ash ratio greatly affect the recycled aggregates mechanical properties. The results show that the compressive strength prediction of the recycled aggregate concrete is predictable with a very high accuracy using the proposed ANN-based model. The proposed ANN-based model can be used further for optimising the proportion of waste material and other ingredients for different targets of concrete compressive strength.

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Mechanical Properties and Permeability of Recycled Aggregate Concrete at Low Water/Binder Ratio

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.477.16 ◽

2011 ◽

Vol 477 ◽

pp. 16-22 ◽

Cited By ~ 3

Author(s):

Gai Fei Peng ◽

Qi Bin Liu ◽

Zhu Bo Guo ◽

Qiao Xing Hou ◽

Si Qi Cao ◽

...

Keyword(s):

Mechanical Properties ◽

Water Absorption ◽

Experimental Research ◽

Chloride Ion ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Aggregate Concrete ◽

Binder Ratio ◽

Water Binder Ratio

This paper presents an experimental research on mechanical properties and permeability of recycled aggregate concrete (RAC). Concretes at a water/binder ratio of 0.255 were broken into recycled aggregates (RA). A type of thermal treatment was employed to remove mortar in RA. Tests were conducted on aggregate to measure water absorption and crushed values, and on RAC and natural aggregate concrete (NAC) to measure compressive strength, tensile splitting strength, and fracture energy. The results revealed that both gravel damage and mortar attached can significantly influence the water absorption and crushed value of RA. The mechanical properties RAC were obviously lower than those of NAC at an identical mix proportion. Moreover the removal of mortar caused a decrease in mechanical properties. The behavior of the chloride ion penetration of RAC under compressive loading is different that of NAC, which may be related to the flaws of RA. Further experimental research is needed to identify its mechanism.

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