Parent Concrete Research Articles

Development of high strength recycled aggregate concrete-composite effects of fly ash, silica fume and rice husk ash as pozzolans

The world today has started facing bigger problems related to the concrete industry, especially with concrete becoming the most extensively used construction material in the world. At a time like this, where more eco-friendly substitutions are stringent, it calls for a more comprehensive approach in producing recycled concrete from recycled concrete aggregates (RCA). This study is an extension to previous studies involving composite utilization of pozzolans in treating RCA. It investigates on the possibility of using rice husk ash (RHA) along with other pozzolans as a cement replacement, in both stages of aggregate treatment and concrete production. It was observed that through this treatment, aggregate specific gravity was increased to a value of 2.37 which was earlier 2.18 for untreated RCA, 26% and 59% reductions were obtained for water absorption and porosity of aggregates, respectively. Further the concrete which contained RHA in both stages, attained a high strength of 55.4 MPa, even surpassing the control mix containing natural aggregates. The same mix resulted a 12% increase in its surface resistivity. Rapid Chloride Permeability Test (RCPT) and water permeability results also showed substantial improvements when compared to the reference RCA mix. Similar to previous studies involving composite use of pozzolans, improvements in the microstructure of both the aggregates and concrete through the use of RHA resulted in the amelioration of both mechanical and durability properties of concrete. This evidently indicates the possibility of achieving high strengths, even with the use of RCA derived from parent concretes of lower grades.

Evaluation of Characteristics and Building Applications of Multi-Recycled Concrete Aggregates from Precast Concrete Rejects.

The construction industry must meet current environmental requirements, mostly those pertaining to the reduction in construction and demolition waste and the consumption of raw materials. The use of recycled concrete aggregates can be part of the solution, but one question that arises is how many times recyclables can be recycled. This unknown involves other related queries regarding the properties and possible uses of repeated recycled concrete aggregates. This research is derived from the precast concrete industry, where multi-recycling is a pressing need. From good-quality parent concretes, three cycles of recycled concrete aggregates were produced and analysed. The final results are promising due to the good quality of the recycled and multi-recycled concrete aggregates obtained. Not only can they be used in low-level applications (backfilling) as usual, but they can also be used for more demanding purposes, such as graded aggregates, cement-treated road bases and concrete pavements. Their use in structural concrete is feasible, but it will be dependent on the water absorption level and the amount of recycled aggregate substitution. This research proves the viability of multi-recycled concrete aggregates with all of the associated environmental benefits.

An innovative and efficient multi-generation recycling system for waste concrete subjected to freeze-thaw environment: A theory model and case study

The existing researches on the recycled aggregate concrete (RAC) mainly focus on the recycling of waste concrete used in atmospheric environment, while the ones on the recycling of waste concrete subjected to complex environments are seldom reported. Reusing waste concrete in freeze-thaw (F-T) environment relates to the multi-generation recycling system of “high performance parent concrete-waste concrete-recycled aggregates (RAs)-next generation of recycled high-performance concrete (RHPC)-next generation of RAs”. The efficient operation and sustainability of such recycling system depends on not only the performances of concrete, but also environmental load and economic benefits. The optimal balance between performance, environmental load and economic benefits for recycling waste concrete in F-T environment is generally affected by the performance of parent concrete and quality of RAs in the recycling system. Based on the theories of the emergy analysis and life cycle cost of structure, a sustainable design theory model of this innovative recycling system is proposed. In this model, high performance concrete (HPC) or RHPC is chosen as parent concrete and the performances of middle and low-quality RAs are improved by carbonation treatment method to gain high-quality RAs. The feasibility of the theoretical model is verified by the emergy analysis of the data of three-generation RAC, which provides a theoretical basis for the frost resistance quantitative design of multi-generation recycled concrete.

Characterization of Coarse Recycled Aggregates Produced from Concretes with Different Strength Levels

With the acceleration of Urban Renewal Program, particularly in large cities of Turkey, the problem of finding land-fills and eliminating construction waste with the least environmental pollution necessitates its value-added recycling. However, the presence of adhered weak mortar layer, comprising 20-70% of recycled concrete aggregate (RCA), limits the use of RCA or lowers its inclusion level in concrete mixtures. Within the scope of this study, limestone- and basalt-bearing RCA obtained from 6 different concrete mixtures with three different water/cement ratios (0.45, 0.60, 0.70) were prepared and their water absorption, specific gravity, dense and loose unit weight, flatness indices, Los Angeles degradation values were determined. The results showed that, increasing w/c ratio of the parent concrete increased water absorption of the resultant RCA. However, the specific gravity, unit weight, abrasion resistance and flakiness index of RCA were decreased by increasing w/c ratio of the parent concrete.

Comparison of Prediction Models Based on Machine Learning for the Compressive Strength Estimation of Recycled Aggregate Concrete.

Numerous tests are used to determine the performance of concrete, but compressive strength (CS) is usually regarded as the most important. The recycled aggregate concrete (RAC) exhibits lower CS compared to natural aggregate concrete. Several variables, such as the water-cement ratio, the strength of the parent concrete, recycled aggregate replacement ratio, density, and water absorption of recycled aggregate, all impact the RAC’s CS. Many studies have been carried out to ascertain the influence of each of these elements separately. However, it is difficult to investigate their combined effect on the CS of RAC experimentally. Experimental investigations entail casting, curing, and testing samples, which require considerable work, expense, and time. It is vital to adopt novel methods to the stated aim in order to conduct research quickly and efficiently. The CS of RAC was predicted in this research utilizing machine learning techniques like decision tree, gradient boosting, and bagging regressor. The data set included eight input variables, and their effect on the CS of RAC was evaluated. Coefficient correlation (R2), the variance between predicted and experimental outcomes, statistical checks, and k-fold evaluations, were carried out to validate and compare the models. With an R2 of 0.92, the bagging regressor technique surpassed the decision tree and gradient boosting in predicting the strength of RAC. The statistical assessments also validated the superior accuracy of the bagging regressor model, yielding lower error values like mean absolute error (MAE) and root mean square error (RMSE). MAE and RMSE values for the bagging model were 4.258 and 5.693, respectively, which were lower than the other techniques employed, i.e., gradient boosting (MAE = 4.956 and RMSE = 7.046) and decision tree (MAE = 6.389 and RMSE = 8.952). Hence, the bagging regressor is the best suitable technique to predict the CS of RAC.

Fundamental behaviour of recycled aggregate concrete – overview I: strength and deformation

Recycled aggregate concrete (RAC) has received huge amounts of attention in the past two decades. However, there are still many critical problems about fundamental behaviours of RAC, which need to be figured out and which otherwise limit its further sustainable popularisation. Therefore, this series of two overviews rethinks fundamental behaviours of RAC based on the latest literature. In this overview (part I), the strength development and its mechanism, as well as failure patterns of RAC under static and dynamic loading, are explored. Then, the influencing factors and prediction models of elastic modulus, shrinkage and creep of RAC are intensively discussed. It is found that, compared with natural aggregate concrete, the 28 day compressive strength of RAC is lower, whereas the long-term compressive strength of RAC may be higher, which partly depends on the strength of the parent concrete. Furthermore, because the elastic modulus of RAC is often decreased, the drying shrinkage and creep of RAC are always increased. However, the autogenous shrinkage of RAC can be decreased, and also generally develops for above 60 days. Finally, some models have been summarised to better predict the elastic modulus and long-term deformation of RAC.

Geometrical, physical, mechanical, and compositional characterization of recycled concrete aggregates

Recycling, being one of the strategies in minimizing waste, offers three benefits: it lessens the demand for new resources, reduces transportation and production energy costs, and beneficially reutilizes waste, which would otherwise be lost in landfill sites. While it is believed that recycled concrete aggregate (RCA) can be effectively incorporated in new concrete, its use is limited, mostly due to the absence of effective characterization of RCA. Current specifications and characterization methods mostly include only basic parameters such as specific gravity and absorption, which are not necessarily representing critical properties such as mechanical properties, residual mortar content, and freeze/thaw resistance. Many test methods that are currently used for RCA are either not suitable for RCA or present human error in the procedure and thus not accurate and repeatable. The goal of this study is, therefore, to develop a testing protocol to characterize RCA effectively. A set of different test methods were used in this study to evaluate RCA collected from various sources. Test methods to identify aggregate crushing value and residual mortar content were modified to accurately characterize a variety of RCA without excessive variability introduced by human factors. The freeze-thaw resistance test with a modified data analysis protocol proved to be capable of differentiating the level of air-entrainment of parent concrete. Aggregate shape and texture were shown to significantly impact the void content of an aggregate granular matrix. A better understanding of RCA physical, mechanical, and compositional properties was achieved, which is critical in designing new concrete and evaluating the effect of RCA on new concrete. The success of the study will greatly encourage the use of RCA in daily concrete production and ultimately lead to a cleaner and more sustainable concrete production.

Some Remarks towards a Better Understanding of the Use of Concrete Recycled Aggregate: A Review

Research on recycled concrete aggregates (RCAs) has been progressively advanced. Beyond replacing natural aggregates with RCA, discussions have been held on the effect of the parent concrete and repeatedly recycled aggregate concrete. Although it has been reported that RCA can be technically used for structural concrete, due to several other factors, RCA is mainly used for sub-bases. Therefore, identifying these factors is the key to promoting the use of RCA. Therefore, this review study first briefly summarizes the physical and chemical characteristics of RCA compared to natural aggregate, and reviews the effects of parent concrete and repeatedly recycled aggregate on next generation concrete. This study also briefly discusses the RCA standards of various countries and the factors that hinder the widespread use of RCA. The results show that there is a correlation in properties between parent concrete and the next generation concrete, and the properties of concrete decrease when RCA is used repeatedly. In addition, on the basis of the literature review, factors hindering the use of RCA were found to be unstable supply and demand, economic feasibility, and negative perceptions.

Mechanical Properties of Recycled Aggregate Concretes Containing Silica Fume and Steel Fibres.

In this study, the impact of steel fibres and Silica Fume (SF) on the mechanical properties of recycled aggregate concretes made of two different types of Recycled Coarse Aggregates (RCA) sourced from both low- and high-strength concretes were evaluated through conducting 60 compressive strength tests. The RCAs were used as replacement levels of 50% and 100% of Natural Coarse Aggregates (NCA). Hook-end steel fibres and SF were also used in the mixtures at the optimised replacement levels of 1% and 8%, respectively. The results showed that the addition of both types of RCA adversely affected the compressive strength of concrete. However, the incorporation of SF led to compressive strength development in both types of concretes. The most significant improvement in terms of comparable concrete strength and peak strain with ordinary concrete at 28 days was observed in the case of using a combination of steel fibres and SF in both recycled aggregate concretes, especially with RCA sourced from high strength concrete. Although using SF slightly increased the elastic modulus of both recycled aggregate concretes, a substantial improvement in strength was observed due to the reinforcement with steel fibre and the coexistence of steel fibre and SF. Moreover, existing models to predict the elastic modulus of both non-fibrous and fibrous concretes are found to underestimate the elastic modulus values. The incorporation of SF changed the compressive stress-strain curves for both types of RCA. The addition of steel fibre and SF remarkably improved the post-peak ductility of recycled aggregates concretes of both types, with the most significant improvement observed in the case of RCA sourced from a low-strength parent concrete. The existing model to estimate the compressive stress-strain curve for steel fibre-reinforced concrete with natural aggregates was found to reasonably predict the compressive stress-strain behaviour for steel fibres-reinforced concrete with recycled aggregate.

Influence of Grade of Parent Concrete on Recycled Aggregate Concrete Made with Pozzolanic Materials

Reducing, recycling and reuse is becoming a world renowned proverb nowadays. The waste from construction industry is increasing day by day. Two major kinds of waste produced from construction industry are concrete waste and brick waste. The concrete waste produced from different buildings will have different strengths. The purpose of this study is to look into the reuse of concrete waste collected from various buildings in the production of recycled aggregate concrete (RAC). RAC 30 is produced by replacing the natural aggregates with recycled aggregates (RA) derived from granite aggregate concretes GAC30 (RA30), GAC35 (RA35) and GAC40 (RA40) grades of parent concrete. In order to produce sustainable concrete, pozzolanic materials such as fly ash (FA) and silica fume (SF) are used in conjunction with cement at a rate of 20% and 10% respectively, in addition to cement. The influence of strength of different grades of parent concrete (GAC) on production of RAC of grade 30 (RAC 30) is studied. The experimental results show that RA derived from parent concrete grades GAC30 (RA 30) can be substituted fully in place of normal aggregate. The use of 20% FA and 10% SF in place of cement also contributed to the enhanced compressive strength, leading to sustainable concrete in field of architectural construction.

Effect of the maturity of recycled aggregates on the mechanical properties and autogenous and drying shrinkage of high-performance concrete

The high cement content of high-performance concrete (HPC) results in improved strength, but also in large shrinkage. The substitution of natural aggregates (NA) with recycled aggregates (RA) notably affects these properties in conventional concrete. This study intends to analyse the effect of the content of RA and their maturity (time elapsed between casting and crushing of the parent concrete from which RA are obtained) on these properties of HPC. To this end, five mixes were manufactured with 0%, 25%, and 100% of coarse and fine RA of different maturities, 7 days (early-age RA) and 6 months (matured RA). The mechanical properties and the autogenous, drying, and total shrinkage of all mixes were determined. Both the increase of RA content and the lower stiffness and strength of early-age RA relative to matured RA worsened the mechanical behaviour of HPC. Regarding shrinkage, the lower stiffness and higher water absorption of matured RA compared to NA decreased autogenous shrinkage by 20%, but increased drying and total shrinkage. The lower stiffness of early-age RA and their shrinkage amplified all types of shrinkage of HPC around 10–20%. Nevertheless, the hydration of their unhydrated cement particles during the mixing process reduced those increases from what was expected. Total shrinkage of early-age recycled aggregate HPC could be estimated from the shrinkage of both a HPC mix of identical composition but with matured RA and the parent concrete. Overall, it can be concluded that RA’s maturity affects the mechanical performance and, especially, the shrinkage of HPC, so it should be considered when using this type of aggregate.

Performance Assessment of Ultra-High Durability Concrete Produced From Recycled Ultra-High Durability Concrete

The purpose of the work reported in this paper is to assess the performance of recycled ultra-high durability concrete (R-UHDC), produced using different fractions of recycled aggregate obtained from crushed ultra-high durability concrete (UHDC), as a substitute for the natural aggregate. Four different recycled ultra-high durability concrete (R-UHDC) mixes were designed and manufactured with a reference mix based on the natural aggregate and three mixes with the natural aggregate replaced using recycled UHDC according to two percentage replacement values (50 and 100%). The effect of environmental degradation of the recycled parent concrete was also addressed, using recycled aggregates subjected to accelerated carbonation (replacement percentage equal to 50%). The work has been conducted in the framework of the activities of the Horizon 2020 ReSHEALience Project in ultra-high durability concrete. One key objective of the project was to formulate the concept and experimentally validate the performance of ultra-high durability concrete for structures and infrastructures exposed to extremely aggressive scenarios. The ReSHEALience consortium has defined UHDC as a “strain-hardening (fiber-reinforced) cementitious material with functionalizing micro- and nano-scale constituents especially added to deliver high durability in the cracked state under extremely aggressive exposure conditions.” In this context, the research was conducted to investigate the potential of recycling the UHDC mixes, developed and validated in previous research and employing them as a partial or even total replacement of the natural fine aggregate in the production of new UHDC. This supports the cradle-to-cradle approach in life cycle engineering applications. The research confirmed the effective regeneration of new UHDC based on the recycled aggregate obtained from crushed UHDC, attaining the required rheological characteristics, mechanical properties (compressive strength, flexural strength, and toughness), and durability performance (chloride penetration resistance, chloride migration, water capillary suction, and resistivity). This work is intended as the first step toward the sustainability assessment of the end of life of UHDC materials and structures and the potential of recycled UHDC for new structures and retrofit structural applications.

Effect of strength of parent concrete on the mechanical properties of recycled aggregate concrete

The effect of quality of original concrete, from which coarse recycled concrete aggregate particles were derived, on mechanical properties of three grades of recycled aggregate concrete (RAC) has been investigated for the following two weight replacement levels of natural coarse aggregates (NCA) with the recycled aggregates: 50% and 100%. The original concrete samples made with natural coarse aggregates were designed for 28-day nominal cube crushing strengths of 20 MPa, 40 MPa and 60 MPa. The results indicated that the grade of original concrete did not have a significant effect on the mechanical properties viz. compressive strength, splitting tensile strength and flexural strength of the three grades of RCA concretes of this investigation. All the aforesaid properties were inferior to those of the control concrete made only with NCA. However, in case of the high-strength parent concrete, the mechanical properties of the resultant RAC were superior as compared to RAC made with normal and medium strength parent concrete.

Understanding the influence of properties of fine recycled aggregates on recycled concrete

Scarcity of fine natural aggregates suitable for concrete, the pollution caused by their mining and the great environmental impact produced by the final disposal of waste concrete, have all motivated several studies about their use as recycled aggregates for concrete, particularly the fine fraction. The use of fine recycled concrete aggregates (FRCAs) is directly linked to the feasibility of obtaining target properties in concrete. Agreement about FRCA's technical viability has not yet been achieved. In this paper, the properties of FRCA associated with different features of the parent concrete and with the performance of recycled aggregate concrete prepared with them were analysed. The results show that the FRCA paste content is not linked to the compressive strength level of the parent concrete. In addition, the total water-to-cement ratio in recycled aggregate concrete seems to have a greater influence on concrete performance compared with quality and composition of FRCA.

Quality Improvement of Recycled Aggregate Concrete using Six Sigma DMAIC Methodology

Recycled aggregates (RA) are obtained from construction and demolished waste, laboratory crushed concrete and concrete waste at RMC plants. The concrete made from recycled aggregate is known as recycled aggregate concrete. The use of recycled aggregate is very beneficial to the environment in civil works. Its usage also helps in financial saving as the cost of transportation and production energy cost of natural coarse aggregate (NCA) is reduced. In India, the recycled aggregate application in lower grade concrete work is observed. However, the effect of recycled aggregate on the strength and durability of concrete restricts its use in higher-grade work. This paper presents a series of tests carried out on recycled coarse aggregate (RCA) and recycled coarse aggregate concrete (RCAC) and test results are compared with the NCA and parent concrete made from NCA. Tests were carried out as per IS code and concrete was prepared using a two-stage mixing approach in the concrete mix design. M30 concrete mix of four RCAC samples was tested at 28 days of curing and in comparison with parent concrete, it is found that on an average compressive strength is decreased by 12.89% at 28 days curing. Adhered mortar increases the porosity of the recycled aggregate and forms a weak zone between aggregate surface and mortar. In addition, test results showed the defects in recycled aggregate and helped to identify the area where concentration is necessary to improve the quality of recycled aggregate using six sigma DMAIC methodology. Total of 12 defects were found in the process and raw material. Statistical analysis was used to evaluate the performance of all the mix made with RCA.

Understanding the behavior of recycled aggregate concrete by using thermogravimetric analysis

The physio-chemical changes in concrete mixes due to different coarse aggregate (natural coarse aggregate and recycled coarse aggregate (RCA)) and mix design methods (conventional method and Particle Packing Method (PPM)) are studied using thermogravimetric analysis of the hydrated cement paste. A method is proposed to estimate the degree of hydration (α) from chemically bound water (WB). The PPM mix designed concrete mixes exhibit lower α. Recycled aggregate concrete (RAC) mixes exhibit higher and α after 7 d of curing, contrary to that after 28 and 90 d. The chemically bound water at infinite time (WB∞) of RAC mixes are lower than the respective conventional concrete mixes. The lower WB∞, Ca(OH)2 bound water, free Ca(OH)2 content and FT-IR analysis substantiate the use of pozzolanic cement in the parent concrete of RCA. The compressive strength of concrete and α cannot be correlated for concrete mixes with different aggregate type and mix design method as the present study confirms that the degree of hydration is not the only parameter which governs the macro-mechanical properties of concrete. In this regard, further study on the influence of interfacial transition zone, voids content and aggregate quality on macro-mechanical properties of concrete is needed.

Effect of Parent Concrete on the Performance of Recycled Aggregate Concrete

Recycling concrete construction waste is a promising way towards sustainable construction. Indeed, replacing natural aggregates with recycled aggregates obtained from concrete waste lowers the environmental impact of concrete constructions and improves natural resource conservation. This paper reports on an experimental study on mechanical and durability properties of concretes casted with recycled aggregates obtained from two different parent concretes, belonging to two structural elements of the old Cagliari stadium. The effects of parent concretes on coarse recycled aggregates and on new structural concretes produced with different replacement percentages of these recycled aggregates are investigated. Mechanical properties (compressive strength, modulus of elasticity, and splitting tensile strength) and durability properties (water absorption, freeze thaw, and chloride penetration resistance) are experimentally evaluated and analyzed as fundamental features to assess structural concrete behavior. The results show that the mechanical performance of recycled concrete is not related to the parent concrete characteristics. Furthermore, the resistance to pressured water penetration is not reduced by the presence of recycled aggregates, and instead, it happens for the chloride penetration resistance. The resistance to frost–thawing seems not related to the recycled aggregates replacement percentage, while an influence of the parent concrete has been assessed.

Utilisation of Ultra-High Performance Fiber Reinforced Concrete(UHPFRC) for Retroffiting – a Review

Retrofitting has become a proven method for improving the load carrying capacity of existing concrete structural elements subjected to high mechanical loading, ageing or aggressive environments. Ultra-High Performance Fiber Reinforced Concrete (UHPFRC)is a relatively new generation of cement-based retrofitting material with a very high compressive strength and low permeability attributed to its tightly packed microstructure, also displaying excellent bonding ability with normal structural concrete. It has the potential to eliminate various problems caused by other retrofitting methods like FRPs or externally bonded steel plates as a result of the mismatch of stiffness with parent concrete. This study presents an overview of UHPFRC focusing on its properties, design, applications and challenges. The performance of UHPFRC concrete mix is greatly influenced by the type and degree of packing of its constituents in the cementitious matrix, necessitating the need for optimisation. Strength properties are very much higher when compared to that of conventional concrete alongside with increased durability aspects. The retrofitting technique showed an enhancement in the load carrying capacity of deteriorated structures. Therefore, UHPFRC can be considered as a practical solution to improve the sustainability of buildings and other infrastructural components. However, as a retrofit, there are some concerns regarding the loss of ductility. This broadens the need for methods to improve its ductility. This paper presents the state-of-art review of existing literature that deals with the retrofitting/rehabilitation of structures using UHPFRC. Altogether, the paper aims to expand the awareness regarding UHPFRC which was otherwise hindered, owing to limited design codes.

Predicting the contribution of recycled aggregate concrete to the shear capacity of beams without transverse reinforcement using artificial neural networks

Although many researchers have studied the shear and flexural behavior of recycled aggregate concrete (RAC) beams, code provisions have not been modified yet to take RAC into account. Therefore, the slow development of code provisions to govern RAC usage limited their widespread use as a construction material for concrete structures. Several factors control the shear behavior for RAC beams and make it different from conventional concrete (CC) beams, such as recycled aggregate content and properties of parent concrete. The main objective of this study is to demonstrate the efficiency of using Artificial Neural Networks (ANNs) in predicting concrete contribution in the shear capacity of RAC beams. The study presents an appropriate model that can predict the experimental value of concrete contribution in shear resistance for RAC beams without transverse reinforcement when knowing the values of 6 inputs (recycled aggregate content, shear span-depth ratio, beam width, beam depth, longitudinal tensile steel ratio, and compressive strength at 28-days) using the intelligent adaptive ANNs based on a database comprised of 231 data points collected exclusively from structural literature. It is found that the proposed ANNs model showed satisfactory results when verified against the calculated values of the concrete shear strength calculated using common-used models existed in literature and code provisions, where the maximum variation for the present ANN model was about 8%. In particular, a comprehensive parametric study was conducted and discussed in detail to investigate the effect of various key parameters on the value of the concrete shear strength and the shape of the behavior. The results demonstrated that ANNs are capable of predicting the shear strength for beams cast with RAC without transverse reinforcement. A sensitivity analysis for the predicted concrete shear strength was conducted to give a better understanding of the effect of the key parameters (inputs).

Los Angeles index and water absorption capacity of crushed aggregates

Abstract The mechanical and physical properties of the crushed aggregate have been studied. The properties of crushed aggregate, which produced from recycled aggregate concrete is not discussed in the literature yet despite it could be a choice in some circumstances like in case of demolishing the structures that already constructed by recycled aggregate concrete. Twenty-two types of self-compacting high-performance concrete made by coarse natural aggregate and coarse recycle concrete aggregate have been crushed and their properties have been studied. The main findings of the present study that, the Los Angeles index and water absorption of crushed aggregate is affected by the coarse recycled concrete aggregate dosage in its parent concrete, as well as, incorporating cement replacing materials in parent concrete help to enhance the abrasion resistance of crushed aggregate.