Equivalent Mortar Volume Method Research Articles

A review of mixture design and preparation methods for high-performance recycled aggregate concrete

Recycled aggregate concrete (RAC) has been widely investigated for recent decades, during which there are a great deal of findings on the modification of RAC to overcome the drawbacks of RA, i.e. high absorption and low strength. In this paper, four methods for designing and preparing RAC are reviewed, including the particle packing method (PPM), equivalent mortar volume (EMV) method, two-stage mixing approach (TSMA) and distributing-filling coarse aggregate (DFCA) process, and their effects on the properties of RAC is compared to reveal the effective approaches to high-performance preparation of RAC. Among these methods, only TSMA presents a positive effect on the workability of RAC. In terms of the properties of hardened RAC, TSMA improves the compressive strength and penetration resistance by densifying the ITZs around RA, and the developed TSMAsc containing silica fume exhibits better efficiency in improving the properties of RAC. The EMV method and DFCA process are beneficial to the compressive strength, elastic modulus and volumetric stability of RAC, and the effectiveness of the DFCA process is superior to the EMV method, indicating that enhancing the coarse aggregate interlocking effect is an effective approach to obtain high-performance RAC. Furthermore, the combination of TSMA and EMV methods can synthesize the enhancements of ITZs and coarse aggregate interlocking effect, contributing to a further improvement in the properties of hardened RAC. It is conceived that the TSMA and DFCA process can be integrated as a promising combination to realize the high performance of RAC.

Effects of replacement ratio and particle size distribution of recycled coarse aggregate on mechanical properties of concrete designed using equivalent mortar volume method

AbstractThe equivalent mortar volume (EMV) mixing method has been proposed to prepare recycled aggregate concrete (RAC) with comparable mechanical properties to those of reference natural aggregate concrete (NAC). Previous studies primarily focused on the mechanical properties of EMV concrete with a single replacement ratio of recycled coarse aggregate (RCA). This paper investigates how the mechanical properties of EMV concrete vary with the replacement ratios and particle size distributions of RCA. Five different RCA replacement ratios and two RCA particle size distributions were assessed. A material demand coefficient was principally proposed to quantify the contribution of the EMV mixing method to reduce the environmental impact; the maximum RCA replacement ratio was suggested to obtain sufficient workability of EMV concrete using an effective sand ratio; a drying shrinkage model was theoretically proposed for EMV concrete accounting for the drying shrinkage of residual mortar. The obtained results indicated that the compressive strength and elastic modulus properties of EMV concrete decreased with increasing RCA replacement ratios; using the effective sand ratio of EMV concrete, comparable mechanical properties to those of reference NAC could be obtained for EMV concrete; the proposed shrinkage model was consistent with the available experimental data.

Uniaxial mechanical behaviors of recycled coarse aggregate concretes cast with conventional and equivalent mortar volume methods

Among the various kinds of adjustment methods to improve the material properties of recycled aggregate concrete (RAC), equivalent mortar volume (EMV) method is widely considered as economic and effective. This is mainly because that only an extra content of natural aggregates (NAs) is needed to be added in the mixture during fabricating RAC. To objectively evaluate the method, this study conducted a series of discrete element mesoscale simulations to illustrate and compare the mechanical behaviors and failure mechanisms for conventional and EMV methods designed RAC samples under uniaxial loadings. Particularly, the influences of the replacement ratio of RAs, the mixture’s water-to-cement ratio and the spatial location of coarse aggregates on the two RACs’ strength and deformation characteristics were analyzed. Additionally, generic expressions used for estimating the mechanical properties of conventional and EMV methods cast RAC samples were also tried to be established in the article. It was found by this study that: (a) As the replacement ratio grows, both the conventional RAC’s compressive strength and elastic modulus reduce monotonously, however, the tensile strength’s variation trend is highly dependent on the relative strength of new-to-old mortar; (b) Regardless of the RAC’s water-to-cement ratio, an EMV design method can always improve the elastic modulus of RAC effectively; (c) When the new mortar strength is lower than that of old mortar, adopting an EMV mix-design method notably improves the RAC’s tensile and compressive strengths, however, if the old mortar strength is obviously smaller, the EMV method’s enhancement to the concrete’s strength is limited; (d) Variabilities for compressive and tensile strengths of EMV method designed RAC samples are commonly higher than those of conventional RAC samples; and (e) Uniaxial mechanical property of RAC sample cast either using a conventional or EMV method can both be predicted with a same formulas.

A Novel Mix Design Method for Mixed Recycled Coarse Aggregate Concrete

Recycled aggregates extracted from the construction and demolition waste of brick and concrete building are mixed recycled aggregates (MRA), which comprise concrete recycled aggregate (CRA) and brick recycled aggregate (BRA). The components of coarse aggregate used in concrete incorporated with MRA are natural aggregate (NA), CRA, and BRA. Due to the complex component of coarse aggregate used in mixed recycled aggregate concrete (MRC), the conventional mix design method is not suitable for MRC. The increase of coarse aggregate heterogeneity, larger total mortar volume of MRC, and the weaker strength of CRA and BRA are the primary differences between MRC and natural concrete (NC). There is no literature to propose a mix design method suitable for MRC with regard to the defects mentioned previously. To address this issue, a novel mix design method was proposed. First, the minimum density difference (MDD) method was proposed to minimize the density difference between fresh mortar and the MRA of MRC, so as to improve the homogeneity. And then the mortar volume in MRC is equal to that of NC by using the equivalent mortar volume (EMV) method. Finally, the minimum paste theory is combined with MDD and EMV methods to determine the parameters of mix proportion, so as to compensate for the defect of too little cement paste content caused by the EMV method. The experimental results showed that when the water:cement ratio is 0.5, compared with the conventional concrete mix design method, the proposed mix design method can increase the compressive strength and elastic modulus by 5% and 22.8%, respectively, and reduce the heterogeneity degree and shrinkage value (90 days) by 8.5% and 23.4%, respectively. When the water:cement ratio is 0.65, the compressive strength and elastic modulus increased by 4% and 33.5%, respectively, and the heterogeneity degree and shrinkage value (90 days) decreased by 28.44% and 23.7%, respectively. The proposed mix design method also consumed a lesser quantity of cement.

Drying Shrinkage and Rapid Chloride Penetration Resistance of Recycled Aggregate Concretes Using Cement Paste Dissociation Agent.

In the present study, a recycled concrete aggregate (RCA) coating treatment using a cement paste dissociation agent (CPDA) with different mixing methods was newly incorporated in RCA concrete mixtures. First, a preliminary test program was conducted to determine the proper dosage of the CPDA solution throughout its RCA concrete test results from compressive strength, flexural strength, and elastic modulus. Then, a series of experimental tests were carried out to investigate the effect of RCA coating treatment, different mixing method such as the equivalent mortar volume (EMV) method and conventional method, and different RCA replacement ratios on durability test results of RCA concrete such as drying shrinkage values and rapid chloride penetration test (RCPT) values. The test results showed that all RCA concretes mixed with the coated RCAs were found to be workable regardless of different mix methods, with the slump and air contents of all the mixes being almost identical. All the concrete specimens, which were mixed with the coated RCAs with CPDA solution, represented lower drying shrinkage and RCPT values than those mixed without RCA coating treatment, regardless of different mix proportioning methods or RCA replacement ratios. This holds for the concrete specimens proportioned with the EMV method, regardless of different RCA replacement ratios.

Mineral Addition and Mixing Methods Effect on Recycled Aggregate Concrete.

This paper presents influence of treatment and mixing methods on recycled aggregate concretes (RAC) designed regarding various techniques. Absolute Volume Method (AVM) according to TS 802, Equivalent Mortar Volume Method (EMV), silica fume (SF) as a mineral addition were considered in the design of concretes. In total, four groups of concretes were produced in the laboratory: (1) natural aggregate concrete (NAC) designed with AVM as control concrete, (2) RAC designed with AVM as control RAC, (3) RAC with SF as a mineral addition designed with AVM as treated RAC and (4) RAC designed with EMV as treated RAC. The tests were performed at 28th days and the statistical analysis were made on the test results. According to the results, EMV and SF increased the compressive strength of concretes and this resulted an increase in the strength class of concrete. A significant statistical difference between the concretes were determined. According to multiple comparison analysis, it was found that especially there was a significant relationship among NAC, RAC and RAC-EMV. In addition, it was recommended that EMV and AVM with 5% SF could be used in the design of RAC rather than AVM only to achieve the target strength class C30/37.

Modeling and predicting chloride diffusion in recycled aggregate concrete

Application of recycled aggregate concrete (RAC) in engineering practice today remains relatively limited. One of the main reasons may be that the material’s durability has not been comprehensively understood. No sufficiently accurate formulas are available for predicting its resistance to chloride infiltration. This study was therefore designed to investigate the commonest factors influencing chloride penetration in RAC using mesoscale finite element models. The variables of interest were the geometric shape of coarse aggregate pieces, their location distribution, the volume content of recycled material, the relative strength of the old to new mortar, the adhering content of old mortar, the bonding property of interfacial transition zones (ITZs) and the mixing method used. After performing a series of numerical simulations, a genetic programming (GP) method was lastly adopted to establish an explicit expression for correlating the RAC’s effective chloride diffusivity with the identified key factors. Numerical results indicate that the RAC’s diffusion coefficient was negligibly influenced by the aggregate shape or the old ITZ property, and commonly grows with increasing water-to-cement ratio, the amount of old mortar, the new ITZ’s diffusivity as well with the replacing content of recycled aggregates. Equivalent mortar volume method can efficiently decrease the material’s chloride diffusivity, especially at low water-to-cement ratios in the attached mortar. Finally, the expression provided by the GP method can adequately predict all these trends and is very convenient for investigating the RAC’s chloride diffusion performance.

Cohesion coefficient of structural concrete made with recycled concrete coarse aggregate

The cohesion coefficient of structural concrete made with recycled concrete coarse aggregate (RCA) was evaluated independently for the first time, through push-off tests having no clamping force across the shear plane, and compared with the cohesion coefficient of structural concrete made with natural coarse aggregate (NCA). Both conventionally compacted and self-compacting concretes were made with RCA and NCA as coarse aggregates. To achieve the best structural quality, concretes made with RCA were proportioned based on the equivalent mortar volume (EMV) principle instead of percentage replacement of NCA with RCA commonly followed in most of the earlier studies. Twelve transversely unreinforced push-off specimens, three from each of the four varieties of concrete, were tested to failure. Cohesion coefficients determined from analytical and finite-element modelling of the push-off tests were found to be in close conformity with each other, and the experimentally found cohesion coefficients were reasonably close to, though not in exact conformity with, the theoretical values. Nevertheless, the experimental results clearly established that RCA concrete when proportioned by the EMV method is not inferior to NCA concrete in terms of cohesion contribution to shear strength.

Evaluation of conventional and equivalent mortar volume mix design methods for recycled aggregate concrete

The use of recycled aggregate concrete (RAC) is undoubtedly on the increase and further research is required for more appropriate mix design methods. This paper presents the result of investigations into the mix design of RAC. The study examined experimentally two conventional and one unconventional mix design methods. The conventional methods include the absolute volume approach according to the American Concrete Institute (ACI) standard and the Department of Environment (DoE) concrete mix design method given by the British specification. The unconventional method is a new technique dubbed “Equivalent mortar volume (EMV)” method developed to incorporate both fine and coarse recycled aggregates for RAC production. A total of four mixes were designed as follows: (1) natural aggregate concrete regarded as the reference mix using the ACI guide, (2) RAC using the ACI guide, (3) RAC using the DoE guide and (4) blended aggregate concrete using the EMV guide. Fresh concrete properties were tested, and twenty concrete cubes and eighteen cylinders were produced accordingly and tested after curing by water immersion for density, compressive strength, tensile splitting strength and water absorption. The results showed that the EMV mix design method used significantly lesser amount of cement to achieve a RAC of higher strength than those obtained from its comparable conventional methods even with original natural aggregates. This is the first work on mix design of RAC incorporating both coarse and fine crushed concrete aggregates carried out using the EMV method. This research highlights that the ACI and DoE mix design method guides should be reviewed and amended appropriately, before adopting them for RAC mix design.

The equivalent mortar volume method in the manufacturing of recycled aggregate concrete

The equivalent mortar volume method in the manufacturing of recycled aggregate concrete

Effect of Different Types of Recycled Concrete Aggregates on Equivalent Concrete Strength and Drying Shrinkage Properties

Residual mortar attached to recycled concrete aggregate (RCA) always leads to a decrease in Young’s modulus and an increase in the drying shrinkage of RCA concrete, mainly due to an increase of total mortar volume. To overcome this inherent problem, the modified and equivalent mortar volume (EMV) methods were proposed by researchers. Despite the comparable test results, both models are still subject to the slump loss problem. Thus, under the same W/C (water to cement ratio) ratio and slump condition, this study assessed the influence of the modified EMV mix method on RCA concrete properties. A total of six mixes were proportioned using the modified EMV method with three different RCAs. Test results show that the concrete mixed with RCA produced from old PC concrete sleepers exhibited compressive strength, Young’s modulus, and flexural strength values within 2% variation, equivalent to those values of the companion natural aggregate concrete. In other mixes, compressive strength was found to decrease to 11–20%. It was observed that for 100% replacement of RCA mix, Young’s modulus increased to 10% and drying shrinkage increased to 8% only, while for 50% replacement of RCA mix, Young’s modulus decreased to 8% and drying shrinkage dropped to 4%.

Mechanical strength and drying shrinkage properties of RCA concretes produced from old railway concrete sleepers using by a modified EMV method

This study aims to assess the mechanical strength and shrinkage properties of recycled concrete aggregate (RCA) concretes produced from old railway pre-stressed concrete (PC) sleepers. PC sleepers with compressive strength of 50 MPa grade, originally manufactured with a maximum size of 20 mm coarse aggregate, were crushed into 25 mm RCAs. A total of six mixes were prepared for typical structural concrete, using the modified equivalent mortar volume (EMV) as well as the conventional ACI mix design method. Comparable values of the elastic modulus and drying shrinkage properties of RCA concrete were achieved from the test results, relative to those of the companion natural aggregate concrete. The use of RCA produced from old PC sleepers is thus proven to be promising when RCA production is targeted for coarse aggregate in structural concrete.

Eco-efficient low cement recycled concrete aggregate mixtures for structural applications

Research has shown that good quality recycled concrete aggregates (RCA) can be produced for structural applications if the aggregate properties are properly considered in the mix design, especially the residual mortar content (RMC). Previous studies on RCA have generally used mixes with moderate to high cement contents, which negates many of the environmental and economic advantages of this material. In this study, the equivalent mortar volume (EMV) method was used to develop RCA mixes with the aim of minimizing new cement content by accounting for the RMC already present, thus improving binder efficiency. Conventional RCA mixes (i.e. 25 and 35 MPa compressive strengths) containing low cement content were developed without any chemical or mineral admixtures. A modified EMV method was proposed to overcome challenges encountered in the fresh state and an optimized 35 MPa mix was developed with a low binder intensity of 9.2 kg/m3·MPa−1.

Freeze\u2013Thaw Resistance and Drying Shrinkage of Recycled Aggregate Concrete Proportioned by the Modified Equivalent Mortar Volume Method

To evaluate the effect of the mix proportioning method on drying shrinkage and freeze-and-thaw resistance of recycled concrete aggregate (RCA) concrete, two series of concrete mixes were made using the modified equivalent mortar volume (EMV) method and the conventional ACI method. In this study, different sources of RCAs were manufactured from on-site plants on air bases and at a commercial recycling plant. Keeping the total mortar at the same level, concrete mixes were proportioned by the modified EMV method, using different scale factors: S = 1 (with RCA substitution of 23%), S = 2 (with RCA substitution of 47%), and S = 3 (with RCA substitution of 73%). It was assumed that the residual mortar volume in the RCA concrete was represented in the sum of the volume of mortar and the volume of aggregate, in variance to the scale factors. Test results showed that the modified EMV method for all the mixes yielded the drying shrinkage property of the RCA concrete comparable to that of the companion concrete with natural coarse aggregate. On the other hand, it was observed in the freeze-and-thaw test that the modified EMV method could be marginally applied to the limited condition with S = 2.

Structural Performance of Reinforced RCA Concrete Beams Made by a Modified EMV Method

This study aims to show the effect of a modified equivalent mortar volume (EMV) method on the flexural performance of recycled concrete aggregate (RCA). To verify this, an experimental study was carried out firstly by testing fresh and hardened material properties of RCA concrete specimens made by two different mixture design methods, i.e., the modified EMV method and the conventional American Concrete Institute (ACI) method. The flexural performance of five reinforced recycled concrete (RRC) beams mixed with different mixture designs was then investigated. Test results confirmed that the elastic moduli of the RCA concrete specimens made using the modified EMV method are greater than those of the conventional ACI mixture, while the drying shrinkage tended to decrease. The ultimate strengths of RRC beams mixed with the modified EMV method are as much as five percent greater than that achieved with the conventional ACI mixture.

Mechanical properties of recycled aggregate concrete proportioned with modified equivalent mortar volume method for paving applications

The equivalent mortar volume (EMV) mix design method, which was originally proposed by Fathifazl et al., was successfully verified in their previous studies for concrete mixes containing coarse recycled concrete aggregate (RCA). However, especially for paving concrete mix, which is typically proportioned with a marginal amount of sand, the nature of the EMV mix proportions leads to a far lower amount of sand. Thus, a modified EMV proportioning method is proposed, assuming that the residual mortar (RM) volume VRMRAC in RCA concrete (RAC) can be represented as the sum of the volume fraction of mortar VRMaRAC and the other volume fraction of coarse aggregate VRMbRAC. To verify this modified EMV method, four series of concrete mixes were made using the modified EMV mix design, along with the original EMV and the conventional mix designs, with various sources of RCAs. For each mix, the slump, air content, compressive strength and elastic modulus were measured. Test results show that the modified EMV method yields modulus properties comparable or superior to those of similar mixes made with natural coarse aggregates or those of conventional mixes with RCA. Furthermore, it is demonstrated that this modified method applies well to paving concrete mixes, regardless of the absorption capacity of RCA.

Mechanical Strength Properties of RCA Concrete Made by a Modified EMV Method

This study used two types of Recycled Concrete Aggregates (RCAs) with the same original virgin aggregate, but with different amounts of residual mortars. To verify that the mechanical properties of the concrete were affected by changing the unit volume of residual mortar, fresh mortar, and total mortar of the concrete, a series of paving concrete mixes were made using a modified equivalent mortar volume (EMV) mix design, along with a conventional American Concrete Institute (ACI) mix design. The test results showed that the RCA concrete with the conventional mix design, which led to a prominent decrease in compressive strength and elastic modulus at each age, had 10% greater total mortar volume than that with the modified EMV mix design. As for the conventional ACI mix, it appears that the replacement ratio of RCA and the volume of the residual mortar in RCA directly affect the modulus of elasticity as well as the compressive strength of concrete. However, for the modified EMV mix, the modulus of elasticity of the concrete may be increased to be equivalent to the companion concrete with natural aggregate by controlling the new mortar volume so that the total mortar volume remains the same regardless of the RCA replacement ratio. It was observed that the smaller new volume requirement makes the RCA paving concrete more environmentally friendly and economically profitable.

Shear capacity evaluation of steel reinforced recycled concrete (RRC) beams

The applicability of some major concrete design standards and other pertinent methods to calculate the concrete contribution to the shear resistance of reinforced recycled concrete (RRC) beams without stirrups is investigated. Results of a relatively comprehensive experimental program are used to compare the actual shear strength of the tested beams with their corresponding predicted values. The concrete mixes for the RRC beams were proportioned by the so-called Equivalent Mortar Volume (EMV) method. The method is predicated on the fact that recycled concrete aggregate (RCA) is a composite material, comprising mortar and natural aggregate, and the volumetric content and properties of each phase must be quantitatively accounted for when proportioning concrete mixes containing RCA. The test variables included in the test program are shear-span/depth ratio, beam size, RCA source, and coarse aggregate type. The results show that the shear capacity of a RRC beam is comparable, or sometimes superior, to that of a companion beam made of conventional concrete. The analyses performed in the current investigation show, contrary to previous findings, that existing shear design methods, such as the ACI and CSA codes methods, are applicable to RRC beams, provided the EMV method of mix design is used.

Durability of recycled aggregate concrete designed with equivalent mortar volume method

Abstract Results of a comprehensive investigation about the durability of structural-grade concrete made with recycled concrete aggregate (RCA) are presented. The RCA-concrete mixes were proportioned using a new concrete mix design method, termed the equivalent mortar volume (EMV) method. The EMV method is based on the hypothesis that RCA is a composite material comprising mortar and natural aggregate; therefore, when proportioning a concrete mixture containing RCA, one must account for the relative amount and properties of each the two components and adjust both the fresh coarse aggregate and fresh paste content of the mix accordingly. Tests were conducted to study the freeze–thaw, chloride penetration and carbonation resistances of the mixes proportioned by the EMV method and by the conventional method. Results of the test showed that RCA-concrete mixes proportioned by the EMV method have higher resistance to freeze–thaw action, chloride penetration and carbonation than those designed with the conventional method, and they satisfy the current requirements for concrete exposed to severe environments.