Virgin Aggregates Research Articles

A Study on Properties of Concrete Made with Processed Granulated Blast Furnace Slag as Fine Aggregate

This study focusses on understanding the influence of processed granulated blast furnace (PGBS) slag on fresh and hardened state properties of concrete. Nowadays, metallurgical slags are being explored as alternative materials to natural virgin aggregates in concrete. Before using any such material in concrete, it is important to understand its influence on properties of concrete. In this study an attempt has been made to use granulated blast furnace slag from a local steel plant as a substitute to natural sand in normal concrete. The study mainly focusses on understanding the influence of different replacement ratios and suitability of slag replacement ratios higher than 50% in normal concrete. The blast furnace slag used in the present study was processed using a vertical shaft impactor to modify the particle shape and enhance its aggregate properties. The replacement was done at 50%, 75% and 100% by mass of natural sand in the concrete mix. The concrete properties such as slump, compressive strength, splitting tensile strength and flexural strength, were studied at all the replacement ratios.

Asphalt Mixtures Containing RAS and/or RAP: Relationships Amongst Binder Composition Analysis and Mixture Low Temperature Cracking Performance

As the price of asphalt binder continues to rise, state agencies are looking for sustainable ways to reduce the cost of asphalt pavements without compromising performance. One such alternative is the use of reclaimed asphalt pavement (RAP) and/or recycled asphalt shingle (RAS) to replace virgin binders and aggregates in asphalt mixtures. To better understand low-temperature cracking resistance of asphalt mixtures containing RAP and/or RAS, 11 asphalt mixtures with various combinations of RAP, RAS, and recycling agent were evaluated. Thermal stress restrained specimen test (TSRST) was performed to evaluate asphalt mixtures’ low-temperature cracking resistance. Saturate-aromatic-resin-asphaltenes (SARA), gel-permeation chromatography (GPC), and Fourier transform infrared spectroscopy (FTIR) were conducted on extracted binders from the 11 corresponding mixtures for analyzing the molecular compositions of the asphalt binders. In addition, dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were carried out to determine the rheological index (R) and difference in critical temperatures (Tc), respectively. It was consistently observed from the inter-comparisons of test results that the addition of RAS, RAP, and RAs adversely affected the low-temperature properties of both the asphalt binders and mixtures studied herein. Improvement in low-temperature properties of asphalt binder and mixture was observed when a softer virgin asphalt binder (PG 58-28) was used in lieu of the control styrene-butadiene-styrene modified PG 70-22 binder. It was also found that the molecular components fractionated from GPC have better correlations with mixtures’ low-temperature cracking performance parameters compared to that from SARA and FTIR analysis. Further, it was concluded that the use of RAS and RAP in asphalt mixtures increased the larger molecular weight species in asphalt binders (i.e., asphaltenes), which contributes to stiffening of asphalt binder and mixtures at low temperatures and, in turn, impairs the low-temperature cracking resistance of asphalt binders and mixtures.

A System for Real-Time Measurement of Moisture in Aggregate Mixes During Asphalt Production

In asphalt plants, moisture fluctuations in aggregate stockpiles present a problem for process control. To improve the production process, real-time methods of monitoring aggregate moisture in stockpiles, cold feed bins, and on conveyor belts have been used with varying levels of success. This paper presents a field-evaluation of the accuracy of a real-time measurement system for measuring moisture content of virgin aggregate mixes moving on a conveyor belt for asphalt production. This system uses nuclear techniques, with no components in contact with the material flow or the belt, to determine the moisture content. Due to its use of low activity radioisotopic sources and a safe design, the system is categorized as a ‘generally licensed’ device by the US Nuclear Regulatory Agency imposing minimal regulatory burden on US plant owners. This measurement system was evaluated during the 2015 and 2016 production seasons at a continuous-type asphalt plant in Wisconsin, USA. Based on the study, the moisture measurement system showed a good sensitivity to moisture in aggregate mixes with 0.9% wt. response to a 1.0% wt. change in moisture. It also showed a good measurement precision of 0.1% wt. at one standard deviation for a 20 second averaging. Over one thousand samples, with limestone as the main aggregate type, were collected from the belt and were used for comparing the moisture measurements from the new system to that by the oven drying method. For the two methods, the correlation of determination was 0.69 and the difference in moisture content was 0.10 ± 0.35% wt. at one standard deviation. The new method did not show dependence on the nominal maximum aggregate size of the mixes.

Homogeneity evaluation of hot in-place recycling asphalt mixture using digital image processing technique

Hot in-place recycling (HIR) allows 100% reuse of reclaimed asphalt pavement (RAP) directly on a construction site. However, the homogeneity of the HIR is difficult to be evaluated due to the complexity of the material composition and construction process. In this study, in view of the homogeneity of the HIR can be reflected by the mixing quality of virgin and RAP aggregates, the homogeneity of virgin and RAP aggregates was investigated. Firstly, the Marshall test specimens of an HIR asphalt mixture were prepared and saw-cut, and the microstructure of each cross section was extracted using digital image processing (DIP) technique, including image enhancement, iterative threshold segmentation and maximum between-class variance (OTSU threshold), retention of the green channel, and image morphology. Then, each cross section of the specimen was divided into 36 regions of equal area by an annular segmentation with sector segmentation. Based on the coefficient of variation in the area ratio of the virgin aggregate to RAP aggregate, a homogeneity coefficient of HIR asphalt mixture was proposed. Another nine groups of Marshall specimens were prepared and cut, and the homogeneity coefficient of each group was calculated. The results showed that the virgin and RAP aggregates in the cross section could be effectively identified due to different gray values by retaining the green channel. The characteristics of the virgin and RAP aggregates could be comprehensively described using annular segmentation combined with sector segmentation. The related macro qualitative test showed that the aggregate in the asphalt mixture could be accurately extracted by the threshold segmentation method based on annular segmentation combined with the OTSU method. The homogeneity could be accurately and quantitatively evaluated by a homogeneity coefficient based on the area ratio of the virgin and RAP aggregates in each cross section. An improvement in the homogeneity of the virgin and RAP aggregates was achieved with an increase in the heating temperature of RAP and mixing time. However, no further improvement was noticed as the heating temperature and mixing time increased. In short, the quantitative homogeneity evaluation index of virgin and RAP aggregates presented in this study, reflecting the homogeneity of HIR asphalt mixture, is helpful for controlling the quality of the HIR asphalt pavement.

Performance and viscoelastic assessment of high-recycle rate cold foamed bitumen mixtures produced with different penetration binders for rehabilitation of deteriorated pavements

The paper investigates the influence of the binder penetration grade on the volumetric, mechanical and viscoelastic properties of cold recycled mixes with foamed bitumen. Cold recycled mixtures produced with foamed bitumen differ significantly from other bituminous paving materials (e.g. hot mix asphalt) in terms of aggregate coating and bonding with the bituminous binder. What is more, hydraulic binders usually contribute to the strength of those mixtures. These factors result in a decreased viscoelastic response of cold recycled mixtures, which may impact the sensitivity of these mixtures to the type of binder used, which has not been thoroughly studied yet. The main body of the conducted experiments included complex stiffness moduli measurements under cyclic uniaxial compressive loading, supplemented by assessment of air void content, indirect tensile strength, resistance to moisture damage, indirect tensile stiffness and static creep modulus. The composition of investigated mixtures with high rate of recycled materials was designed to reflect a common scenario in rehabilitation of deteriorated pavements subjected to low and medium traffic loads. The three utilized binders were graded as 35/50, 50/70 and 70/100 penetration road paving bitumen, and were added as foamed bitumen in 2.5% amounts to the cold mix. The recycled mixes contained 50% of reclaimed asphalt pavement material, 30% of reclaimed crushed stone base and 20% of virgin aggregates. A hydraulic binder in form of Portland cement was used as a binding agent in amounts of 2%. Each of the investigated mixtures exhibited significantly distinct results in terms of air void content, indirect tensile strength and creep stiffness modulus. The performance of mixtures with 50/70 and 70/100 binders was similar in indirect tensile stiffness moduli and complex stiffness moduli. It was found, that the binder type had significant effects on the compactability of investigated mixtures, which resulted in different mechanical performance. At the same time the influence of the binder type on the viscoelastic properties of the cold mixtures was attenuated. It was concluded that the limited influence of the binder used was caused by the significant amount of reclaimed asphalt material in the evaluated mixtures and the effects of cementitious binding of the Portland cement. The results showed that a wide range of penetration grade bitumen can be used for producing cold recycled mixtures with foamed bitumen with only minor effects on their performance and viscoelastic properties.

Characterization of Classified Indian Reclaimed Asphalt Pavement (RAP): In-Situ and Lab Density, Bitumen Content and Gradation Characteristics.

Reclaimed asphalt pavement (RAP) is the term given to removed and/or reprocessed pavement materials containing asphalt and aggregates. These materials are generated when asphalt pavements are removed for reconstruction, resurfacing, or to obtain access to buried utilities. When properly crushed and screened, RAP consists of high-quality, well-graded aggregates coated by asphalt cement. Process of utilization of reclaimed asphalt pavement (RAP) is called recycling of asphalt pavement. RAP material is generated when old, damaged pavement materials are milled and crushed for addition as a component to new mixtures placed in the pavement structure. Historically, old pavement material was removed and disposed of in landfills. As land filling these materials has become less practical and more expensive and the availability of quality virgin materials declines, the addition of RAP to pavement mixtures has become more and more prevalent. Recycling of pavement material can be done as an in-place process or a central plant process. The in-place process combines the reclamation, mixing, lay down, and compaction procedures into a single paving train in the field. In-place recycled materials are typically used for base or binder courses and are typically overlaid with a surface course. The central plant process involves stockpiling RAP at the asphalt plant, which is then mixed with virgin materials at the plant and trucked to the construction site for lay down and compaction. Use of RAP in road construction will reduce depletion of virgin aggregates resources and also overcome to disposal problem of bituminous wastes. It is required to access properties of RAP aggregate and recovered bitumen before using in actual road pavements. RAP samples collected and a series of tests are performed for characterization and performance evaluation of selected RAP samples of different groups. In this study characterization of RAP limited to in-situ and lab density along with bitumen content and gradation of RAP classified in different groups. Results of this study will be beneficial in job mix formula (JMF) design with varying percentage of RAP to be use in bituminous layer in flexible pavements. This study is a step towards sustainable developments with green road construction i.e. construction of flexible pavement with environmental protection and conservation of natural resources.

Energy and Environmental Life Cycle Assessment of Sustainable Pavement Materials and Technologies for Urban Roads

Recycled and low-temperature materials are promising solutions to reduce the environmental burden deriving from hot mix asphalts. Despite this, there is lack of studies focusing on the assessment of the life-cycle impacts of these promising technologies. Consequently, this study deals with the life cycle assessment (LCA) of different classes of pavement technologies, based on the use of bituminous mixes (hot mix asphalt and warm mix asphalt) with recycled materials (reclaimed asphalt pavements, crumb rubber, and waste plastics), in the pursuit of assessing energy and environmental impacts. Analysis is developed based on the ISO 14040 series. Different scenarios of pavement production, construction, and maintenance are assessed and compared to a reference case involving the use of common paving materials. For all the considered scenarios, the influence of each life-cycle phase on the overall impacts is assessed to the purpose of identifying the phases and processes which produce the greatest impacts. Results show that material production involves the highest contribution (about 60–70%) in all the examined impact categories. Further, the combined use of warm mix asphalts and recycled materials in bituminous mixtures entails lower energy consumption and environmental impacts due to a reduction of virgin bitumen and aggregate consumption, which involves a decrease in the consumption of primary energy and raw materials, and reduced impacts for disposal. LCA results demonstrate that this methodology is able to help set up strategies for eco-design in the pavement sector.

Influence of recycled concrete aggregate treatment methods on performance of sustainable warm mix asphalt

This study aimed to investigate the usability of Recycled Concrete Aggregate (RCA) in warm mix asphalt (WMA) as the implementation of sustainable construction technology. Five replacement rates (0%, 25%, 50%, 75%, and 100%) were tested for the coarse fraction of virgin aggregate (VA) with 3 types of RCA: untreated RCA, HL-treated RCA, and HCL-treated RCA. Scanning electron microscopy (SEM) analyses were performed to investigate the surface morphology for both treated and untreated RCA. The optimum asphalt cement content for every substitution rate was determined using Marshall mix design method. Thereafter, asphalt concrete specimens were prepared using the optimum asphalt cement content, followed by the evaluation of their performance properties, including the moisture damage, resilient modulus, and permanent deformation characteristics. These properties were assessed using indirect tensile strength and uniaxial repeated loading tests, respectively. It was found that, for mixes with RCA content of 100%, the untreated RCA mixes possess higher OAC than that of treated RCA mixes by 0.26%. The moisture susceptibility was improved in case of HL and HCL treated RCA by 9.09% and 10.34% as compared to untreated RCA. However, the resilient modulus and resistance to permanent deformation for the mixes with 100% RCA were lower than those prepared with VA; the decrement in Mr values are 39.17%, 28.56% and 23.09% for the untreated RCA, HL-treated RCA and HCL-treated RCA, respectively. Finally, the cost, material, and energy-saving implications of RCA were discussed.

Evaluation of Glass Powder-Based Geopolymer Stabilized Road Bases Containing Recycled Waste Glass Aggregate

As the concept of sustainable pavement gains prominence, a growing number of industrial wastes and recycled materials have been utilized in the pavement industry to preserve natural resources. This study investigates the potential use of waste glass powder-based geopolymer cement as a stabilizing agent in recycled waste glass aggregate (GA) bases. Two recycled materials, waste glass powder (GP) and class F fly ash (FF), were used as the raw materials in the preparation of geopolymer. Virgin aggregate (VA) was replaced by GA at varying replacement ratios as the pavement base materials, and the mechanical behaviors before and after geopolymer stabilization were evaluated. Without stabilization, the incorporation of over 10% GA caused significant detrimental effects on the California bearing ratios (CBR) of base materials, which should be carefully managed in pavement construction. However, all geopolymer stabilized samples showed decent strength properties, indicating the effectiveness of geopolymer stabilization. The use of GA reduced the drying shrinkage of base samples, although the mechanical properties were compromised. During the sample preparation, a higher curing temperature and relative humidity resulted in better mechanical behaviors, and the surface of GA could dissolve in alkaline solution and involve in the geopolymerization at 40°C. The microstructure and minerology of geopolymer stabilizer of base materials were characterized by scanning electron microscopy (SEM) and X-ray defraction (XRD) analyses. This study confirmed the promise of using waste glass-based pavement base materials as the greener substitutes and the potential synergy between waste glass recycling and the pavement industry.

Use of Recycled Material in WMA- Future of Greener Road Construction

Sustainable road construction practice requires an asphalt mix technology that is environmental friendly, energy-efficient, economical and protective for humanity and health. India and many other countries are using Hot Mix Asphalt (HMA) technology for asphalt road construction. HMA has several disadvantages like high production temperature (155˚C to 165˚C), which increases Green House Gas (GHG) emissions. These emissions increase Global Warming and severely affect the respiratory system of paving crew workers. Warm Mix Asphalt (WMA) technology can reduce the mixing and compaction temperature by around 30˚C in comparison to HMA. WMA has many advantages over HMA like fuel-saving, reduced emissions, improved visibility at the site, more incorporation of Reclaimed Asphalt Pavement (RAP). RAP is the old aged flexible pavement material that can be recycled back to construct a new pavement. Researchers found two major issues with the use of RAP in asphalt mixes such as high emission during mixing of RAP with virgin aggregate and premature cracking due to aged (stiff) binder. WMA may resolve these two issues, first by reducing binder’s viscosity at lower production temperature (reducing high emissions during production of asphalt mix) and second, reducing secondary aging of RAP aged binder. Some WMA additives also works as rejuvenators and provide good coating. This paper discusses the WMA technology, it’s classification, mix design guidelines for WMA, era of recycling, use of RAP and Reclaimed Asphalt Shingles (RAS) into WMA and role of rejuvenators in WMA.

Neutralization of high pH and alkalinity effluent from recycled concrete aggregate by common subgrade soil.

Use of recycled concrete aggregate (RCA) as highway basecourse material conserves virgin aggregate, reduces energy consumption and CO2 emissions, and may also decrease costs during construction. However, concerns remain over possible negative environmental impacts associated with high pH(>11) effluent from RCA in contact with water. This study examines the reactive transport of high-pH and high-alkalinity water, modeled on RCA leachate, through model subgrade soils. By developing an understanding of the reactions controlling effluent neutralization, this study aims to quantify the change in pH from the discharge site through surrounding subgrade soils. Four types of subgrade soils with a range of mineral composition, Atterberg limits, and cation exchange capacities (CECs) are examined. They include a clayey sand (SC10), low-plasticity clays (M14, SC25), and a high-plasticity clay (CH38). Batch reaction experiments are used to develop kinetic parameters describing the neutralization of high-pH and -alkalinity leachate by clay minerals through mineral dissolution and reprecipitation. Given this information, a reactive transport model incorporating advection, diffusion, and reaction is used to model the change in pH as a function of distance traveled through model subgrade soils and is applied to laboratory-scale column experiments. The rate at which the high pH front travels is directly related to a soil's clay mineral content. Soils with high CECs effectively delay the propagation of hydroxide front by the dissolution of clay minerals. This study demonstrates that common subgrade soils with moderate clay content will effectively neutralize high pH leachate initially produced by RCA.

Characterization of RCAs and their concrete using simple test methods

From a sustainability point of view, the use of recycled concrete aggregate (RCA) in concretes is of great interest in the present day. The original virgin concrete from which RCA is obtained determines the properties of the RCA, and it also controls the durability of recycled aggregate concretes (RACs) produced. In this study, the performance of three sources of RCAs with different absorption, obtained from crushed concrete pavement and stockpiles, were evaluated using various mechanical, thermal and non-destructive durability test methods. Suitability of RCA for cold climates was evaluated using a test method for the resistance of unconfined coarse aggregate to freezing and thawing (CSA A23.2-24A). The mechanical properties of the RACs were assessed with the compressive strength test. Non-destructive durability tests on the RACs included surface and bulk electrical resistivity, ultrasonic pulse velocity (UPV), and volume of permeable voids (ASTM C642, boil test). The effect of RCAs on the thermal conductivity of concrete was also evaluated. All of the measured properties of RACs were compared with a concrete mix containing natural virgin aggregate. Correlations between the absorption of aggregates and measured properties were also established. The test results provide an overall understanding of the feasibility of using different sourced RCAs in concretes.

Experimental study to investigate the performance of cold in-place recycling asphalt mixes

This research work was performed to study the impact of steel slag and limestone virgin aggregates as a substitution for recycled asphalt pavement (RAP) in cold in-place recycling (CIR) asphalt mixes. An anionic slow-setting (SS-1) emulsion was used to fabricate the specimens. Marshall stability and flow test, dynamic creep test and moisture susceptibility test were performed to evaluate the mechanical performance of the CIR mixes. The results of this research showed that the presence of modifier aggregates leads to an increase of Marshall stability, and a decrease in permanent deformation and moisture susceptibility. Furthermore, the additional aggregate contents have a significant impact on the moisture and rutting resistance of CIR mixes. Limestone-modified mixes were more resistant to moisture damage. However, steel slag-modified mixes showed better performance against rutting distress.

Influência da velocidade de carregamento e temperatura no comportamento mecânico de misturas recicladas a frio com emulsão asfáltica e espuma de asfalto

A reciclagem a frio de pavimentos é uma alternativa sustentável para a redução do consumo de materiais virgens e do descarte inadequado de resíduos gerados em obras de restauração. Entretanto, ainda não há um consenso sobre as propriedades mecânicas das misturas recicladas a frio, principalmente em relação ao comportamento viscoelástico. Por meio de simulações computacionais usando o software 3D-Move Analysis, avaliou-se a influência que a velocidade dos veículos e a temperatura de trabalho têm sobre as propriedades mecânicas de um pavimento cujas camadas de base são constituídas por misturas recicladas a frio estabilizadas com emulsão asfáltica (AEM) ou com espuma de asfalto (FAM). Com o objetivo de estudar como variam as deformações longitudinais para um ponto localizado no fundo do revestimento asfáltico, observou-se que os materiais reciclados a frio apresentam comportamento viscoelástico, pois diferentes combinações de velocidade e de temperatura resultam em diferentes distribuições de tensão e deformação na camada de revestimento. Dessa forma, observou-se que a não consideração da presença de viscoelasticidade linear para estes materiais pode vir a subestimar a capacidade de suporte da estrutura.

Evaluation of optimum mixing conditions for rubberized asphalt mixture containing reclaimed asphalt pavement

The use of reclaimed asphalt pavement (RAP) represents an environmentally positive method of recycling besides saving cost. Experience has shown that properly designed hot-mix asphalt (HMA) containing RAP performs as well as HMA produced with virgin materials. Crumb rubber asphalt represents, on the other hand, a promising paving material that recycles waste tires. The combination of the two techniques has promising environmental significance, i.e. recycling asphalt concrete pavement using rubberized asphalt, which remains a virgin research topic. In this paper, microstructure of rubberized asphalt mixture containing RAP was studied to obtain its optimum mixing conditions. Specimens were prepared in the laboratory and scanned by X-ray Computed Tomography (CT) system to identify distribution of the components. An improved Otsu’s algorithm was used to segment the mixture images. The results indicate that the algorithm could effectively solve the uneven brightness problem of scanned images. Statistical indicators were used to analyze uniformity of component distribution. Three mixing time and three mixing temperatures were used in the blending process to evaluate effects of mixing time and mixing temperature on the distribution of mixture component. It was found that distribution of air voids and virgin aggregates are relatively more sensitive to mixing time and mixing temperature. Optimum mixing time is 150 s and it should not be less than 90 s to achieve well distribution of components. Optimum mixing temperature is at least 150 °C.

State of a sustainable drainage system at end-of-life: assessment of potential water pollution by leached metals from recycled pervious pavement materials when used as secondary aggregate.

Sustainable drainage systems (SuDS) have emerged as an effective and attractive approach for stormwater management, prevention of water pollution and flood control due to its sustainable, environmentally friendly and cost-effective approaches. One of the SuDS devices widely used to infiltrate, store and treat surface runoff which allows it to recharge groundwater is the pervious paving systems (PPS). Previous studies have demonstrated relatively high pollution removal efficiencies typically ranging from 98.7% for total hydrocarbons to 89% of COD. Although a small number of the studies have assessed the performance characteristics of the PPS system in long-established installations in terms of retention of pollutants, hydrological features, biodegradation of pollutants etc., none has assessed the risk of potential groundwater and soil pollution by pollutants such as metals retained in the PPS materials either as a disposed waste material (in the case of used geotextiles) or during re-use as secondary aggregates. Thus, this study evaluated potential risks associated with the decommissioning and beneficial use of wastes produced during the disassembly of a PPS. The authors believe that this was the first PPS to be addressed in this way. The method involved the determination of leachable concentrations of 14 metals in the PPS samples made up of extracts from the model profile which included the geotextile fibre (G), dust alone (D), aggregates and dust (AD), aggregates alone (AA) and pavement blocks (P) which were analysed and compared with two different groups of regulatory threshold limits. The results showed that the measured concentrations of all the metals were below the appropriate threshold values for irrigation purposes as specified by FAO and USEPA. Furthermore, results all indicated that the dismantled materials were all below EU LFD WAC limits for inert waste, indicating relative ease of disposal and suitability for use as recycled aggregate. This, admittedly limited data, indicates that recycling of aggregates from demolition wastes arising from end of life PPS would not be limited by the potential leaching of heavy metals, including re-use within another PPS. This would minimise dependence on virgin aggregates and hence reduce rate of exploitation of natural resources and improve sustainability score card of SuDS.

Regression models to predict workability and strength of flowable concrete containing recycled aggregates

Regression models are rigorous computational techniques for developing and optimizing performance of cementitious-based concrete materials used for civil and infrastructure engineering works. This paper is part of a comprehensive research program undertaken to develop regression models that predict the behavior of self-consolidating concrete (SCC) containing recycled aggregates, for given proportioning constraints while minimizing the number of trials. Two series of SCC mixtures prepared with 375 and 450 kg/m3 cement are tested. The water-to-cement ratios varied from 0.5 to 0.38, while the natural coarse aggregates were partially substituted by recycled ones at different rates varying from 0% to 100%. Tested properties include the rheology, passing ability, segregation, bleeding, surface settlement, and 28-days compressive strength. Reported regression models can be of particular interest to concrete researchers and engineering seeking for higher recycling technologies and improved sustainability in construction through conservation of virgin aggregate resources, energy savings, landfill reduction, and reduced CO2 emissions.

Performance evolution of the interfacial transition zone (ITZ) in recycled aggregate concrete under external sulfate attacks and dry-wet cycling

Performance evolution of different types of interfacial transition zones (ITZs) contained in recycled aggregate concrete (RAC) under external sulfate attacks coupled with dry-wet cycling is experimentally studied in the labotrary. Comparisons are made between different ITZs in the erosion products, the morphology changes, and the microhardness evolution. Changes in the pore structure and microhardness of the old and new mortars are also discussed. Test results show that sulfate ions accumulate faster in RAC than in natural aggregate concrete (NAC), while the erosion products are the same. Erosion occurs in all ITZs but the predominant erosion prodcuts are not identical: AFt and gypsum are found in new ITZs (i.e., ITZ1 between the unwrapped old virgin aggregate and the new mortar, and ITZ3 between the old and the new mortars), while in the old ITZ2 (embedded inside RA between the old virgin aggregate and the adhering old mortar), fewer gypsum crystals can be seen; due to the dry-wet cycling, thenardite crystals are generated but mainly in ITZ1 near the exposure surface. It is also found that the size of AFt in ITZ1 and ITZ3 is larger than that in ITZ2. The microhardness of ITZs and cement mortars is found to first increase and then decrease with the growth of the erosion age. The old ITZ2 presents the most stabilized performance thereby manifesting itself better to resist the sodium sulfate attacks compared to the new ITZ1 and ITZ3. The old mortar is inferior to both the new mortar and the ITZs in resisting sulfate attacks at a long erosion age. The new ITZ1 and ITZ3, as well as the old cement mortar, should be thereby identified to be the predominant weak points in RAC under external sulfate attacks, on the micro scale. This paper also suggests enhancing these weak points for the purpose of improving RAC’s resistance to sulfate attacks in dry-wet cyclic environments.

Influence of gradations on performance of emulsified asphalt cold recycled mixture produced using vertical vibration compaction method

In this study, the effects of virgin aggregate content, such as mineral filler, machine-made sand, and coarse aggregate, on the performance of emulsified asphalt cold recycled mixtures (ECRMs) produced using the vertical vibration compaction method (VVCM) are evaluated. The optimum virgin aggregate contents are proposed based on the results. The results show that with increasing mineral filler content (mass fraction <5%), the mechanical strength, rutting resistance and crack resistance of the ECRMs gradually increase, whereas the moisture sensitivity increases initially but gradually decreases, and 3% mineral filler demonstrates the optimum moisture sensitivity compared to reclaimed asphalt mixtures. Further, as machine-made sand content increases, the mechanical strength, rutting resistance, crack resistance and moisture sensitivity of the ECRMs increase initially and decrease gradually, and the aforementioned performance of the ECRMs reaches the peak values when 20% machine-made sand is added, compared to mixtures without the machine-made sand. The mechanical strength, rutting resistance, crack resistance and moisture sensitivity of the ECRMs initially increase and then gradually decrease with the addition of the coarse aggregate. When the coarse aggregate content is 10%–30%, the ECRMs show a good performance, compared to mixtures without the coarse aggregate. To effectively improve the engineering properties of the ECRMs, the proposed optimum content of the mineral filler, machine-made sand and coarse aggregate are 3%, 20% and 10–30%, respectively.

Suitability of Scoria as Fine Aggregate and Its Effect on the Properties of Concrete

The increase in the demand for concrete production for the development of infrastructures in developing countries like Ethiopia leads to the depletion of virgin aggregates and high cement demand, which imposes negative environmental impacts. In sustainable development, there is a need for construction materials to focus on the economy, efficient energy utilization, and environmental protections. One of the strategies in green concrete production is the use of locally available construction materials. Scoria is widely available around the central towns of Ethiopia, especially around the rift valley regions where huge construction activities are taking place. The aim of this paper is therefore to analyze the suitability of scoria as a fine aggregate for concrete production and its effect on the properties of concrete. A differing ratio of scoria was considered as a partial replacement of fine aggregate with river sand after analyzing its engineering properties, and its effect on the mechanical properties of concrete were examined. The test results on the engineering properties of scoria revealed that the material is suitable to be used as a fine aggregate in concrete production. The replacement of scoria with river sand also enhanced the mechanical strength of the concrete. Generally, the findings of the experimental study showed that scoria could replace river sand by up to 50% for conventional concrete production.