Virgin Aggregates Research Articles

Mechanical and physical characteristics of alkali- activated mortars incorporated with recycled polyvinyl chloride and rubber aggregates

One of the ways to achieving net-zero concept in the construction industry is to use alternatives to Portland cement (OPC) and virgin aggregates for concrete manufacturing. Recycled rubber and polyvinyl chloride (PVC) aggregates in conjunction with low-carbon binders can be potentially utilised to substitute natural sand and reduce the negative environmental impacts of OPC. A replacement of natural sand (up to 70% by volume) in alkali-activated materials (AAMs) with recycled rubber and PVC particles derived from tyre waste and insulation coating of electric wires, respectively, was investigated in this study. The performance of developed AAMs was evaluated using a comprehensive testing program including mechanical, physical and microstructure assessments. AAM composites with PVC and rubber particles outperformed natural aggregate composites in terms of thermal resistivity, water absorption, volume permeability voids (VPV), and high-frequency sound insulation. Results showed that 70% PVC mixture achieved the lowest water absorption rate and thermal conductivity with a reduction of 73% and 20%, respectively, compared to the control mixture. A maximum reduction of 34% in VPV was observed in the 70% rubber mixture when compared to the control mixture. In terms of mechanical properties of waste stream aggregates, PVC outperformed rubber. The results showed that 30% replacement of PVC and rubber would produce composites with 7-day compressive strengths of 35 MPa and 25 MPa, respectively, which can be used to produce high-load bearing structures. The Energy-dispersive X-ray Spectroscopy (EDX) was performed to detect chloride leaching from PVC aggregates, where results indicated that no leaching had occurred after more than 90 days of casting. Regarding the carbon emission, the carbon footprint of AAM composites is decreased by using the polymeric fractions in place of sand. The developed composites of this study can be used safely in non-load bearing structural elements with promising physical and mechanical performance.

Flexural performance and life-cycle assessment of multi-generation recycled aggregate concrete beams

To minimize the consumption of virgin aggregates during concrete production, and to utilize the high volume of construction waste, a limited number of studies have been devoted to the potential use of multi-generation recycled aggregate concrete (MGRAC). To date, these studies have been restricted to quantifying aggregate and material properties, and no research has investigated behaviour at the member level or assessed the applicability of code specified design approaches. To investigate the impact of MGRAC at the member level, in this work, four generations of concrete are manufactured, the first using virgin aggregates (VA) and then three subsequent recycled aggregate generations (RA-1 to RA-3) with 100% replacement ratios. The flexural behaviour of MGRAC is tested through a series of small-scale reinforced concrete beams , where for each generation beams with two different reinforcement ratios are tested. Throughout testing, member load-deflection and crack-width are recorded. The study further assesses the feasibility of using standard code approaches to design MGRAC beams at different limit states and quantifies the global warming potential (GWP) of each generation of concrete. The results show member level behaviour at the ultimate limit state is not negatively impacted by the use of MGRAC, but tension stiffening and cracking are influenced at the serviceability limit state. Standard design approaches are able to predict member strength but under predict member deflection. Life-cycle assessment demonstrates little variation in GWP between each generation of concrete manufacture, but as expected, show significant savings in virgin material usage.

Influence of Cotton Knitted Fabric Waste Addition on Concrete Properties

Manufacturing cotton knitted fabric apparel generates a substantial amount of production (pre-consumer) waste. One of the ways to alleviate the environmental impact of this is to use the cotton knitted fabric production waste (CKFW) in concrete, which had the simultaneous benefit of reducing the use of virgin aggregate. The aim of this research was to examine the influence of CKFW on concrete properties, and to explore the possible application of this novel material in the construction industry for the production of precast building elements based on its characteristics. An additional goal was to enhance certain properties of concrete and determine the shortcomings of CKFW concrete. A total of 10 mixes were made and tested. CKFW was used at rates of 1.7% and 3.5% of the total mix volume. All mixtures had the same amount of cement, with three mixes having the addition of silica fume. Crushed limestone was used as the aggregate with different aggregate size combinations. Two types of polycarboxylic ether-based superplasticizer were used. The properties of the fresh mix were determined by the slump method. The ultrasonic pulse velocity, dynamic modulus of elasticity, flexural strength and compressive strength were tested on 28-day-old concrete specimens. The σ–δ diagram is also presented in this paper. We learned that the flexural strength of specimens with CKFW addition was increased by up to 38% but the compressive strength was reduced by up to 20% compared to the reference concrete mix. The CKFW mixtures had higher ductility and permeability. Additionally, silica fume had a positive effect on the concretes with a higher percentage of textiles. The percentages of textile waste used in this study affected the density of concrete in a range of 0–2%. Based on the obtained results, we offer recommendations for further tests and possible applications.

Quantitative Assessment of Road Performance of Recycled Asphalt Mixtures Incorporated with Steel Slag.

Circular utilization of reclaimed asphalt pavement (RAP) has received extensive attention for its economic and environmental benefits. The application of recycled asphalt mixtures (RAM) in the upper layer of asphalt pavement faces the issue of inferior anti-slip performance and durability. This study aims to recycle steel slag as virgin aggregates in RAM and quantitatively evaluate the service performance of RAM with steel slag. Steel slag and basalt RAM were firstly fabricated and the five different RAP contents were involved. Then tests of Marshall stability, indirect tensile strength and Cantabro spatter loss were conducted to investigate the moisture susceptibility of RAM. Moreover, their high temperature stability, crack resistance and skid resistance were characterized. Indirect tensile fatigue test combined with Hamburg wheel tracking test were carried out to discuss the durability of RAM. The comprehensive performance of RAM with steel slag were quantitatively assessed based on an improved radar chart evaluation method. The results show that involving steel slag reveals a remarkable enhancement function on water stability, high and low temperature performance, skid resistance and fatigue resistance of RAM. Steel slag RAM with 50% RAP content demonstrates a rutting depth of 7.60 mm and a creep slope of 2.54 × 10−4, indicating its superior durability in high temperature and water environment. Compared with the comprehensive evaluation function of 0.5336 for basalt RAM with 30% RAP dosage, steel slag RAM reaches 0.7801, which represents its preferable road performance.

Hybrid methods to improve microstructure of recycled concrete and brick aggregate for high-grade concrete production

Carbon-conditioning or chemical permeation methods can provide excellent microstructural improvements to recycled concrete and brick aggregate; however, the applications have their limitations. Further, recycled brick aggregate cannot be effectively carbon-conditioned with conventional methods as it contains only trace amounts of reactive materials. It is therefore a necessity to use hybrid methods involving dual technologies combining carbon-conditioning and chemical permeation for its improvement. This paper is focused on developing a novel hybrid method for improving the microstructural properties of recycled concrete aggregate and recycled brick aggregate for concrete usage. This study conducts particle density, water absorption and crushing value tests to measure the physical improvements achieved with the novel hybrid method, and utilises a variety of chemicals and a reaction chamber for carbon-conditioning for aggregate treatment. The study evinces that both the recycled concrete aggregate and recycled brick aggregate experienced significant improvements, with 10 mm and 20 mm recycled concrete aggregate and 10 mm recycled brick aggregate exceeding the density of virgin aggregate. Magnesium hydroxide plus carbon dioxide (Mg(OH)2 (s) + CO2 (g)) treatment for recycled concrete aggregate and calcium hydroxide plus magnesium hydroxide plus carbon dioxide (Ca(OH)2 (s) + Mg(OH)2 (s) + 2CO2 (g)) treatment for recycled brick aggregate can be considered as potential candidates for optimal hybrid treatment methods.

Durability studies on fly-ash based laterized concrete: A cleaner production perspective to supplement laterite scraps and manufactured sand as fine aggregates

This research aims to produce sustainable concrete by effectively utilizing laterite scraps as fine aggregates in fly ash-based cement concrete and assessing its durability characteristics. This utilization reduces sand extraction, pollution to the environment, and conserves natural reserves by reducing the need for virgin materials. To evaluate the engineering properties, durability properties and sustainable property of laterized concrete, a control mix made with 0% laterite scraps and four mixes made with 25%–100% laterite scraps at 25% intervals with the same high-quality cement, fly ash, and coarse aggregate was used. Due to the influence of clay minerals such as kaolinite and montmorillonite in laterite scraps, the slump values ranged from 85 to 15 mm, with the control mix being more workable than the laterized samples. The combination of 75% manufactured sand and 25% laterite scraps in concrete were found to remarkably enhance the residual compressive strength. A significant increase of compressive strength of about 11% was achieved at replacing 25% laterite scraps at 28 days. Higher replacements of 50%, 75%, and 100% laterite scraps decrease cubes strength by approximately 3%, 15%, and 28%, respectively. From the compressive strength test results, it is quite evident that utilizing laterite wastes reduces the amount of virgin aggregates needed to produce concrete resulting in less natural resource consumption. Moreover, the test results of durability parameters such as water absorption, permeability, sorptivity, drying shrinkage, and rapid chloride penetration of laterized concrete mixes containing 50% replacement recline within the acceptable limits as per standards, confirm their intended performance throughout the specific structural service life. The embodied energy assessment of laterized concrete mixes achieved the most significant reduction of 22.41 MJ/m3, revealing the advantageous role of laterite scraps in reducing energy expenditure.

Analysis of Optimal RAP Content Based on Discrete Element Method

Methods of recycling a large amount of waste asphalt mixture generated in pavement maintenance and decreasing the waste of existing resources are one of the problems that will be solved in the future. In this study, the mechanical parameters of asphalt mixture containing different amounts of RAP were analyzed by discrete element method (DEM), and the reasonable RAP content was discussed in combination with uniaxial compression test results. And it is considered that the contact between different particles will produce the failure of stress transfer between particles with different modulus, and the contact definition between RAP particles and virgin aggregate particles is added to make the discrete element model more in line with the actual situation. The results indicated that the trend of discrete element analysis was consistent with that of the uniaxial penetration test, but there were differences in the specific values. Uniaxial compression test results showed that the optimum RAP content of the recycled asphalt mixture was 30%. The optimal RAP content analysis result from the DEM simulation was smaller than the laboratory test result, and the theoretical optimal RAP content was 28%. The results of this study provide a reference for the mixture design of recycled asphalt mixture.

Life Cycle Assessment of Construction and Demolition Waste Management in Riyadh, Saudi Arabia

Extensive construction augmenting the infrastructure and real estate projects underpin Saudi Arabia’s Vision 2030 of sustainable cities. A part of this struggle involves the transformation of the existing infrastructure together with new construction, which generates a large amount of construction and demolition waste (CDW). In the absence of a structured life cycle assessment (LCA) framework, the waste management companies are planning future scenarios (phased expansions of material recovery facilities to improve the recycling rate) primarily on economic grounds. This study assesses the environmental impacts of the existing and planned CDW management practices of the Saudi Investment Recycling Company in Riyadh City by dint of LCA. Impact 2002+ performs life cycle impact assessment of the base case (45% recycling), four treatments (61, 76, 88, and 100% recycling), and zero waste scenarios. The study demonstrates the benefits of current CDW (mixed soil, concrete blocks, clay bricks, glazed tiles, and asphalt) recycling in terms of avoided impacts of non-renewable energy, global warming, carcinogens, non-carcinogens, and respiratory inorganics potentially generated by landfilling. For the treatment scenario of 100% recycling, CDW conversion into a wide range of aggregates (0–50 mm) can replace 10–100% virgin aggregates in backfilling, precast concrete manufacturing, encasements and beddings of water mains and sewers, manholes construction, non-load bearing walls, and farm-to-market roads. To achieve long-term economic and environmental sustainability, municipalities need to improve source segregation, handling, and storage practices to enhance the existing (45%) recycling rate to 100% in the next five years and approach the zero-waste scenario by 2030. The findings of the present study motivate the generators for source reduction as well as encourage the recycling companies and concerned organizations in the continuous performance improvement of the CDW management systems across Saudi Arabia on environmental grounds, as an addition to the perceived economic benefits.

Identification of the Main Environmental Impact Categories Over the Life Cycle of Hot Mix Asphalt: An Application to Green Public Procurement

Increased environmental awareness has led road agencies to consider the implementation of green public procurement (GPP). Besides sustainability rating systems, environmental indicators can also be implemented in GPP to help road agencies make informed decisions about the environmental impact of the pavement works they procure. A vast literature review revealed that it is still unclear which impact categories are responsible for the majority of the total environmental impact of asphalt mixtures. The objective of this study was to identify the impact categories with the greatest contribution to the total environmental impact of hot mix asphalt so that they can be implemented in the form of environmental indicators in GPP. The scope included conventional and polymer-modified binder and three mix design alternatives: only virgin aggregate, reclaimed asphalt pavement (RAP), and RAP with rejuvenators. The cradle-to-cradle life cycle assessment (LCA) performed showed that global warming (GW), fine particulate matter formation, fossil resource scarcity, and human non-carcinogenic toxicity were responsible for at least 90% of the total impact according to the ReCiPe 2016 hierarchic assessment method. Therefore, a simplified LCA focusing on these four impact categories seems sufficient for the purpose of comparing the environmental performance of alternatives in GPP. It was also found that GW alone accounted for approximately 50% of the total impact, which seems to make GW a good surrogate for the total impact among the asphalt mixtures evaluated. Future work should investigate whether the conclusions from this study still hold up when using secondary materials, lower temperature mixing technologies, or in-situ recycling.

Investigation of using municipal solid waste incineration fly ash as alternative aggregates replacement in hot mix asphalt

The use of un-conventional materials in asphalt pavements is becoming popular as DOTs in many countries started to legislate their in the paving industry. The motive behind this is to get rid of available waste while maintaining or improving the pavement performance Fly ash is among those recycled materials that can be used as a substitute for virgin aggregates inbituminous mixtures. This study investigates the effect of using Municipal Solid Waste Incineration Fly Ash (MSWI-FA) as partial or full replacement of fine aggregates and mineral filler on the performance of asphalt mixtures. . The purpose of the experimental testing program is to determine the optimal MSWI-FA replacement type and percentage to be used in asphalt mixtures. This is done through a series of dynamic modulus tests with different MSWI-FA replacement percentages. The different mixes are then ranked based on their rutting and fatigue cracking potential using simple performance indicators.

Technical Approaches to the Recycling of Reclaimed Asphalt Pavement into Aggregate and Binder

Approximately 99% of reclaimed asphalt pavement (RAP) has been recycled in Japan in recent years. However, the deterioration in quality of repeatedly recycled RAP cannot be prevented through existing methods, nor can sustainability be guaranteed. In addition, it is challenging to procure virgin aggregate and binder. Therefore, to ensure the quality and supply of future recycled hot-mix asphalt, it is necessary to explore sustainable recycling technologies. This study examined the advantages and disadvantages of the technical approaches to the recycling of RAP into aggregate and binder. We develop a recycling technology (separate recycling technologies) that uses hot water to separate and restore aggregate and binders to their initial condition from RAPs. The quality of the aggregate, recovered by the hot water rubbing method at 80 °C and 90 °C, fully satisfies the standard values for virgin aggregate at all temperatures. The aged binders, reacting through a hydrothermal decomposition method (hydropyrolysis), with a reaction temperature of 300–350 °C and a reaction time of 0–15 min, tend to have a significantly improved effect. These results confirm that both the hydrothermal rubbing and hydropyrolysis methods could be beneficial options for establishing separate recycling technologies for RAP.

Performance of concrete materials containing recycled aggregate from construction and demolition waste

The performance of recycled aggregate material from construction and demolition waste can affect concrete material strength that incorporates recycled aggregate in high volume. The current research assesses the overall benefits of recycled aggregate materials from construction and demolition waste from different sources. It evaluates the performance of concrete materials containing recycled aggregate as a substitute for conventional aggregate materials at various rates for coarse and fine aggregate materials. The investigation includes basic laboratory works on the behavior of concrete materials. These tests consist of primary characteristics of the recycled aggregate materials that can determine the material performance while substituting virgin aggregate materials. The substitution rate varies to identify the best version of the materials. It ranges from 0% to 100%, and the data included in the current research work was obtained from site visits to the existing recycling plants in Delhi, India. The maximum replacement rate of recycled aggregate materials to the natural aggregate materials has been used up to 100%, and the effects have been analyzed. The substitution rate is highly dependent on the conditions and purpose of the engineering projects. Concrete materials perform accordingly as it is related to the substitution rates directly.

Optimizing RAP sieving efficiency of linear vibrating sieve using DEM simulation

Producing recycled hot-mix asphalt mixtures (RHMA) requires an adequate stockpile of reclaimed asphalt pavement (RAP). To improve the content of RAP in RHMA and maintain the quality stability of RHMA, crushing and sieving technology was applied to pretreat RAP, which is mentioned in various technical standards across the world. However, the obstacle that affects the RHMA output during continuous production in any real-life project is the low efficiency of RAP crushing and sieving. A model of a three-dimensional, three-layer linear vibrating sieve was established in the numerical software of the Discrete Element Method (DEM) by considering the sieving combination commonly used in engineering. The Linear Model and Linear Parallel-Bond Model were defined for the contact properties of the RAP particles. Based on DEM simulation, the influence of sieving parameters such as vibration amplitude and frequency as well as inclination and length of the sieve mesh were evaluated by sieving efficiency. Furthermore, the optimal RAP sieving parameters were obtained and verified in the project. The results show that the sieving efficiency first increases and then decreases with an increase in amplitude, frequency, and inclination; however, the length of the sieve mesh has little effect on the sieving efficiency. The order of influence of the different parameters on the RAP sieving efficiency is as follows: amplitude > frequency > inclination > length. The optimal sieving parameters of RAP were 20 Hz, 3 mm, and 10°, respectively, for frequency, amplitude, inclination. The optimum sieve inclination of virgin aggregate was 20° higher than that of RAP. The deviation between the sieving efficiency of the DEM simulation test and the plant sieving test was within 15%, indicating that the DEM simulation had high accuracy. The study could be of interest to sieving plant manufacturers, pavement maintenance sector, and construction contractors.

Mechanical Properties of Cold Mix Asphalt (CMA) Mixed with Recycled Asphalt Pavement

From the perspective of sustainability and environmental concerns, the use of cold-mix asphalt (CMA) and recycled asphalt pavement (RAP) is more advantageous than the use of hot mix asphalt (HMA) and warm mix asphalt (WMA). Some researchers used a mixture of CMA and RAP to improve the mechanical properties of pavement and made it more economical. However, only a few studies have focused on using a high content of RAP—particularly 100% RAP—as the virgin aggregate. Therefore, this study aims to analyse cold-mix asphalt (CMA) using 100% recycled asphalt pavement (RAP) instead of virgin aggregate raw materials and to determine the best mixture for the production of environmentally friendly asphalt. It is necessary to investigate the performance of CMA mixed with RAP in terms of the resilient modulus, indirect tensile strength, fatigue and rutting resistance. In this study, the percentage of bitumen emulsions added is 2%, 2.5%, 3%, 3.5%, and 4%, along with 100% RAP material. The results indicate that the fatigue life of the RAP mixture increased by 49.34% with the addition of bitumen emulsion (BE) from 2% to 4%, while the wheel tracking test experienced a decrease in rutting depth along with an increase in BE dose of 4%, which was 9 mm. The mixture containing 4% asphalt emulsion has the best performance. The results suggested that increasing the BE dosage increases the resistance against rutting and fatigue.

UTILIZATION OF RECLAIMED ASPHALT PAVEMENT (RAP) WITH PLASTIC WASTE (Dry Process) AS ROAD PAVEMENT MATERIAL IN FLEXIBLE PAVEMENT USING HOT MIX ASPHALT (H.M.A.) TECHNIQUE (Marshall Stability Method)

The Reclaimed Asphalt Pavement Material (RAP) is obtained from the reclamation process from the bituminous roads, which are not commonly used for further construction, and dumped near the site. The RAP can be used as an aggregate. RAP also contains bitumen binder, which can be utilized in pavement construction. Since a decade plastic waste is used in road construction. Plastic waste safe disposal is also a big challenge to humans for protecting our environment and eco-system. There is no literature or research on the combined uses of RAP with Plastic waste. This project uses two waste materials, Reclaimed Asphalt Pavement Material (RAP) and Plastic waste for the construction of flexible pavement. Designing Dense Bituminous Macadam (DBM) Grading-II, which is now commonly used for flexible pavement on National Highway (NH), and State Highway (SH). Prepared samples with Reclaimed Asphalt Pavement material (RAP) and virgin aggregate, satisfying grading and specifications of aggregate as per MoRTH recommendations using Job mix formula (JMF). Bitumen Grade VG-30 used for binder. Adding Plastic waste as per IRC SP:98 2022[2] on hot aggregate (Dry Process) starting from 6% and increment of 2% up to 12% by weight of Optimum Bitumen Content (OBC). Assuming plastic will function as a binder. Comparing samples properties i.e., density, Marshall stability, flow value, air voids, voids in mineral aggregate, [VMA], and voids filled by bitumen [VFB]. From comparison found that RAP - 25% and Plastic waste 8% has satisfied all criteria of design & showed higher stability. The use of Reclaimed Asphalt Pavement Material (RAP) can save mines and disposal problems. Plastic waste uses in road construction also solves plenty of problems for the environment. The use of both waste materials can reduce the construction cost of the highway project. Key Words: Plastic waste, Marshall, stability, flow, energy, . environment ,Reclaimed Asphalt Pavement, RAP.

Evaluation of mechanical properties and structural behaviour of concrete pavements produced with virgin and recycled aggregates: an experimental and numerical study

ABSTRACT Due to the large-scale use of materials in highways, the sustainability of materials has attracted considerable interest for years. In this respect, significant effort has been spent investigating the use of recycled aggregates in concrete pavements. This study has been carried out to fill the gap in the structural performance of recycled aggregate concrete pavements. First, properties of concrete mixtures, produced with virgin, recycled concrete and recycled brick aggregates were experimentally measured, and the results were compared. Then, finite element analyses were done by following a novel methodology that considers the well-known previous works. Results showed that replacement of coarse aggregates with recycled aggregates decreases the mechanical properties in various amounts. Due to the resulting performances, for the same slab thickness, decreased maximum stress, increased deflection and stress ratio values were found for recycled aggregate mixtures. Additionally, higher thicknesses and material requirements were found for recycled aggregate concrete for a similar life. Despite the decreased performance and increased material requirements, the use of recycled aggregates in pavements can still be a viable alternative for countries with limited natural resources and landfills. Therefore, based on the findings, several important discussions and suggestions were presented for future works.

Eco-friendly design of Warm mix asphalt (WMA) with recycled concrete aggregate (RCA): A case study from a developing country

Warm Mix Asphalt (WMA) is a type of asphalt concrete with growing notoriety in the paving industry since they generate economic and environmental benefits compared to traditional alternatives. Various techniques have been studied to maximize the sustainability components present in WMAs, including the Recycled Concrete Aggregate (RCA) inclusion as a partial replacement for virgin aggregates. WMA with various RCA contents has been examined in several case studies from the mechanical, performance, and economic perspectives. Nonetheless, thorough environmental studies have so far been limited, mostly assuming that the use of RCA reduces the environmental burden due to being a recycled product. However, this consideration is not entirely correct since RCA increases the optimal asphalt content. Therefore, excessive RCA contents generate a counterproductive environmental effect. The difficulty associated with the estimate of how much RCA is considered detrimental could explain why detailed environmental evaluations have not been developed on this type of material. This study develops a trade-off methodology based on the Life Cycle Assessment (LCA) technique and statistical analysis to determine the maximum RCA content to be incorporated into WMA without generating greater environmental impacts. The main contributions of this investigation to the literature are establishing the first approach to optimize the design of WMA with RCA inclusion and identifying the variables that directly affect the contaminating potential of this type of asphalt mixture.

Application of Sieve Analysis to Estimate Recycled Binder Availability

One of the challenges of engineering asphalt mixtures containing reclaimed asphalt pavement (RAP) is uncertainty in the proportion of the total recycled asphalt binder that is available to interact and blend with the virgin asphalt, referred to as the recycled binder availability. The industry presently lacks a practical method to quantify RAP binder availability. Research has shown that the primary source of unavailable recycled binder is agglomerations of adhered RAP particles. The binder bound within the agglomerations is unavailable to contact and therefore blend with virgin asphalt. Building on this knowledge, this study establishes a practical method to quantify the extent of RAP agglomeration and, in turn, RAP binder availability by comparing the gradation of recovered RAP aggregates with that of the RAP itself. A size-exclusion method and corresponding predictive equation to estimate RAP binder availability from the high-temperature performance grade of recovered RAP binder and mixing temperature were also assessed. Four RAP sources were evaluated. Each RAP stockpile was paired with virgin aggregates from the same plant that the RAP was sourced at to produce eight mixtures. Tracer-based microscopy measurements within the eight mixtures were generally in good agreement with the estimations of recycled binder availability using sieve analysis. Implementing the size-exclusion method was challenging with local aggregate, and estimates using the predictive equation yielded in some cases good but overall poorer agreement with the measurements of recycled binder availability from tracer-based microscopy compared with the sieve analysis approach.

A prediction model for compressive strength of CO2 concrete using regression analysis and artificial neural networks

Concrete is a very effective material for the construction of buildings and infrastructure around the world. Unfortunately, typical concrete is a large contributor to CO2 emissions and consumption of natural reserves. CO2 Concrete allows the mitigation of these downfalls by carbonating recycled aggregate, reducing CO2 emissions, reusing crushed masonry materials and conserving virgin aggregate. CO2 Concrete can also be considered reliable as its compressive strength can be accurately predicted by both regression analysis and artificial neural networks. The artificial neural network created for this paper allow accurate prediction of the compressive strength for CO2 Concrete. The artificial neural network exhibited a strong relationship with the experimental specimens, revealing a multiple R of 0.98 and an R square of 0.95. The artificial neural network was also validated by 22 laboratory validation concrete mixes. The artificial neural network displayed an average error of 1.24 MPa or 3.43% in the validation mixes with 59% of concrete samples within 3% error and 77% being within 5% error. The successful prediction of compressive strength of CO2 Concrete can help a greater mainstream use of the green material.

Reclaimed Asphalt Pavement (RAP) as an Unbound Base Course Material: A Mechanistic Design Approach Based on Multi-stage Repeated Load Triaxial Tests

Reclaimed asphalt pavement (RAP) and blends of RAP with virgin aggregate (VA) were characterized in this study to be utilized as base course aggregate. Multi-stage and single repeated load triaxial (RLT) tests were conducted in the laboratory to characterize the materials. The results from these tests were used to develop a mechanistic design approach that is suited not only for virgin but also for recycled materials that are prone to excessive plastic deformations under repeated loads. The design approach presented in this study allows the users to select different pavement structure configurations in terms of base course and HMA thicknesses, where the selected configuration can withstand the repeated loads without undergoing significant permanent strains. Such design approach was achieved with the laboratory tests that were conducted with variety of stress ratios (σ1/σ3) that represented different pavement layer configurations and beyond. Principles of shakedown theory were utilized to define the boundaries of plastic shakedown, creep shakedown, and incremental collapse. This study demonstrated that the use of failure and plastic shakedown boundaries were crucial to the proposed mechanistic design approach.