Reduction In Compressive Strength Research Articles

Characterizations and quantification of freeze-thaw behaviors of recycled brick aggregate concrete

The use of recycled brick aggregates (RBAs) in concrete could provide sustainable solution in construction industry by reducing the consumption of natural resources and protecting the environment by saving landfill sites. However, the use of RBAs is uncommon due to limited available research studies investigating its mechanical and durability behavior, especially the freeze-thaw (FT) behavior. Despite a few studies on FT resistance of RBA concrete (RBAC), the FT deterioration mechanism in RBAC is not fully understood, particularly at the microscale. This lack of understanding hinders the widespread adoption of RBAC in sustainable construction practices, particularly in cold regions. Therefore, this study investigates the FT deterioration mechanism in RBAC using macro and microscale experiments and proposes a Weibull damage model to accurately describe the damage variation in RBAC. RBAC specimens with different water-cement (w/c) ratios of 0.65, 0.5 and 0.35 and RBA replacement levels of 0%, 25%, 50% and 100% were produced and tested under rapid FT cycles. Surface scaling, mass loss, relative dynamic modulus of elasticity, and compressive strength reduction were evaluated. X-ray computed tomography (XCT) was used to characterize pore structure and microcracking alterations during FT cycles. The results showed that the deterioration of RBAC increased with the increase in RBA replacement level. XCT revealed increased porosity and microcracking within the RBA particles, which was linked to the significant damage observed in RBAC compared to reference concrete. Quantitative analysis of pore size distribution before and after FT cycling revealed a substantial increase in small pores (<1 mm3) in RBAC. The proposed Weibull distribution damage model accurately described the damage variation in RBAC with different w/c ratios. This study provides new insights into multiscale FT deterioration mechanisms affecting RBAC, aiding in optimizing RBAC mix designs to balance sustainability and durability.

Circular production of recycled binder from fly ash-based geopolymer concrete

This paper presents an investigation into the potential of recycling fly ash - based geopolymer concrete, to produce a recycled binder for circular re – use as starting material. The aforementioned would be a significant advantage over Portland cement which is non – recyclable, owing to its irreversible hydration. The experiment conducted involved crushing and sieving old parent fly ash – based geopolymer concrete, to separate out the paste from aggregate. The paste was then pulverized using a ball – mill to produce the recycled aluminosilicate starting material, herein referred to as recycled geopolymer cement (RGPC). Fly ash was blended with 0 to 100% RGPC, then used to prepare fresh geopolymer paste and mortar mixtures activated using a binary alkali activator consisting of sodium hydroxide and sodium silicate. Samples were cast then cured at 23 or 80 °C. The various tests done were workability, setting time, compressive strength, splitting tensile strength, drying shrinkage, water absorption, and volume of permeable pores. Analytical studies were done using X – ray diffraction, scanning electron microscopy and Fourier – transform infrared spectroscopy. Results showed that incorporation of RGPC into geopolymer mixtures generally led to reduction of workability and setting time, reduction of compressive and tensile strength, along with increase in drying shrinkage. It was, however, found that up to 60% RGPC can be incorporated into geopolymer mixtures while maintaining adequate performance suitable for structural applications. Unlike Portland cement, hardened geopolymer concrete is evidently recyclable to produce a circularly re – usable binder.

Influence of subsurface temperature on cryogenic fracturing efficacy of granite rocks from Kazakhstan

Liquid nitrogen (LN2) is a new stimulation technology suitable for geothermal energy extraction that increases porosity, permeability, and overall contact area in candidate subsurface formations. It is considered appropriate for hot dry rock (HDR) reservoirs. Due to the significant temperature difference between hot rock and cryogenic fluid, extensive thermally induced cracking is anticipated upon contact, which is helpful in future water-steam cycling operations. To examine the degree of rock integrity failure in granite samples as a function of exposure mode, different procedures were followed for comparison. In particular, three commercial granite samples from three regions of Kazakhstan: Kapal-Arasan, Zhylgyz, and Zheltau, were heated to various elevated temperatures prior to immersion in LN2 with variations in freezing time (FT) and numbers of freezing-thawing cycles (FTC). Samples were examined by various methods to quantify the impact of the cryogenic fracturing process. Compression, acoustic emission (AE), and permeability tests were performed on granite with different starting temperatures ranging from 200 °C to 500 °C. Permeability enhancement was generally in the range of 50-90 %. Scanning electron microscopy (SEM) was also used to document the microscopic characteristics of thermally-induced cracks and indicated most induced fractures to be microscale features. Results showed reductions in Unconfined Compressive Strength of LN2-treated samples by up to 76 %. The experimental outcomes demonstrate that LN2 cooling of hot granite induces mechanical rock failure and permeability augmentation. Furthermore, the degree of thermo-fracturing increases with temperature difference and time of LN2 treatment in both freezing time and freezing-thawing cycle methods. This is the first systematic study of its kind to test three commercially available granites from Kazakhstan with this combination of examination tools to assess alternate cryo-fracturing methods for geothermal energy prospecting and contact area enhancement.

Carbonation of calcium sulfoaluminate belite binder: mechanism and its implication on properties

Calcium sulfoaluminate belite (CSAB) binder is an alternative low CO2 binder. CSAB cement has ye’elimite as the primary clinker phase which hydrates to form monosulfate or ettringite as the main hydration product. The hydration and mechanical characteristics of CSAB cement and PC-CSAB blended cement have been reported in several studies; however, studies on the durability characteristics such as carbonation are limited. This study focuses on evaluating the microstructural and mechanical alterations due to carbonation in a CSAB binder system and understanding the underlying mechanism of development of the carbonation front. CSAB binder was found to carbonate rapidly compared to PC binder, accompanied by a reduction in compressive strength. This was attributed to the increase in the pore volume due to the carbonation of the ettringite-rich microstructure, facilitating further ingress of CO2 into the microstructure. The rate of carbonation in CSAB binders diverged significantly from the square root of time model used for PC binders.

Performance of cement mortar mixes containing fine reclaimed asphalt pavement aggregates and zinc waste

Cement mortar mixes were prepared to test the suitability of fine reclaimed asphalt pavement (FRAP) aggregates as a replacement for natural fine aggregates (NFA). With different amounts of NFA (25%, 50%, 75% and 100% by weight) replaced with FRAP aggregates, the mechanical qualities of the mortar mix deteriorated. To counteract this, jarosite – a waste from the zinc industry – was used as a partial replacement for cement (replacements of 5%, 10% and 15%). The jarosite improved the microstructural, mechanical and shrinkage properties. For example, compared with the control mix (100% NFA), the mix containing 25% FRAP aggregates showed a 5.5% reduction in hardened density and a 14% reduction in compressive strength. With the addition of 10% jarosite, there was an increase of 4.85% in hardened density and 7% in compressive strength with respect to the mix containing 25% FRAP aggregates. It is thus suggested that 10% jarosite is used when FRAP aggregates are used to make cement mortar mixes. A cost analysis was also performed. The findings of this work are expected to inspire rational mix design recommendations for mortar mixes including FRAP aggregates, as well as bringing environmental and economic benefits by reducing carbon dioxide footprints.

The Influence of Waste Perlite Powder on Selected Mechanical Properties of Polymer–Cement Composites

The subject of this paper is the influence of the partial substitution of cement with mineral additive on the properties of polymer–cement composites (PCCs). Although there is considerable research on the use of perlite in cement concrete, most of the previous studies were conducted with expanded perlite or ground waste perlite, and there is a lack of results evaluating its suitability with polymer–cement composites. To fill this gap, this paper presents the mechanical characteristic of PCC mortars containing waste perlite powder. The modification consisted of replacing part of the cement with waste perlite powder, a byproduct formed during the expansion and fractionation of perlite. The granulometric characteristics of the powder were compiled, and its specific surface area and density were determined. A chemical composition analysis was also carried out. An aqueous dispersion of styrene–acrylic copolymer was used as a polymer modifier. The proportions (by mass) between the contents of the PCC composite components, i.e., cement/polymer (0 to 20%) and cement/mineral powder (0 to 15%), were used as material variables. The technical characteristics tested included the compressive, flexural, and tensile strengths at 28 and 90 days of curing. The compositions of the tested composites were determined using the statistical planning of the experiment. At a low polymer-modifier content in PCC mortars (2.93%), the tested mechanical strengths decreased by five times, with a 6-fold increase in waste content. For mortars containing more than 10% of the polymer modifier, no effect of waste material powder on the flexural strength was observed, while with relatively minor reductions in compressive strength of 2% and 5% and tensile strength of 4% and 2% were observed after 28 and 90 days of curing, respectively. It was shown that it is possible to use waste perlite powder as an ingredient in construction polymer–cement composites, while there is a limiting waste content, above which there is a deterioration in mechanical properties.

Influence of incorporating fine green foundry sand waste in the production of geopolymers: study of physical and mechanical properties

The aim of this article was to evaluate the physical and mechanical properties of a geopolymeric material developed by replacing metakaolin, a conventional precursor, with fine green foundry sand waste (FGFSW). Substitution ratios of 0% (reference specimen), 5%, 10%, 15% and 20% were used, as well as molar ratios of SiO2/Al2O3 equal to 3.0 and 3.5. The specimens were cured at 7, 14 and 28 days and then tested for compressive strength, water absorption, void ratio, dry density and saturated density. In addition, the specimens were subjected to macrographic tests to assess the geopolymer material. The results showed a reduction in compressive strength as substitution increased. There was also a decrease in density as the substitution increased, as well as an increase in porosity and water absorption in the geopolymer matrix. These effects were attributed to the presence of FGFSW grains which did not take part in the geopolymerization reaction, having a low density and contributing to the reduction in mechanical strength. Finally, incorporating the waste into the production of geopolymers appears to be a possible alternative for disposing of green foundry sand waste.

Physical, strength and acoustic properties of lightweight cement composite with preplaced chemically-treated crumb rubber

The valorisation of waste tyre crumb rubber (CR) as a sustainable construction material can alleviate environmental pollution and save natural aggregate consumption. However, its use in cement composite can result in a significant loss of strength due to weak adhesion and the non-uniform dispersion of CR. To compensate this strength loss, this research aims to investigate the innovative incorporation of chemically treated CR via the preplaced aggregate mixing (PM) method in producing a lightweight cement composite. The CR was treated with different chemicals, namely soaking in potassium permanganate and sulphuric acid solutions. The findings reveal a significant improvement in compressive strength (up to 160%) and water absorption reduction (from 20% to 175%) using the chemically treated CR and PM mixing methods, producing a lightweight cement composite with a density of about 1535 kg/m3. The SEM observation demonstrates the improvement in the CR–paste interface due to the treatment of the CR and the PM mixing methods, and due to the chemical treatment, which improved the wettability of the CR. On the other hand, the sound absorption and noise reduction coefficient of the chemically treated CR lightweight cement composite was almost similar for both the normal mixing (NM) and the PM methods. Overall, the results demonstrate that the CR treatment with sulphuric acid is promising for the PM method to produce a lightweight cement composite.

Optimal Quantity Investigation of Metakaolin and Silica Fume in Production of Durable Acid Resistance Alkali Activated Slag Concrete

The urgent requirement to reduce greenhouse gas emissions during Portland cement production and to enhance the durability of concrete in destructive environments are essential reasons to seek other alternative materials like alkaline activated binders. In this study, the feasibility of producing durable alkali-activated slag-based concrete under deteriorative environmental conditions was studied using 0, 10, 20, 30, and 40% of metakaolin (MK) and 0, 5, and 10% of silica fume (SF) instead of ground granulated blast furnace slag (GGBFS) and optimizing contents through the response surface method (RSM).To evaluate the performance of studied alkali-activated slag-based concrete in an aggressive environment, the permeability and the reduction in compressive strength of alkali-activated slag-based concrete under sulfuric acid attack have been investigated. In addition, the mass change of specimens after exposure was measured. The results indicate that replacing 40% of the slag with metakaolin and 10% with silica fume in alkali-activated concrete has reduced 9% and 34.9% of the compressive strength at 28 days, respectively. Also, increasing MK replacement up to 40% increased the water absorption to 27.8%, but 10% SF replacement reduced it to 17.7%. In addition, the alkali-activated slag-based concrete mass changes after 90 days of acid exposure were 2.3%, while the replacement of slag by 40% of MK and 10% of SF reduced this value to 1.14%. However, it improved the durability performance of alkali-activated concrete against sulfuric acid attacks.

Transverse isotropic compression behavior of aligned steel fiber UHPC produced by electromagnetic field

Aligned steel fiber ultra-high performance concrete (ASF-UHPC) demonstrates transverse isotropic mechanical properties. Specifically, when subjected to compressive stress perpendicular to the fiber orientation, surface cracks emerge proximate to the fiber tips, resulting in a significant enhancement of the material's compressive strength. Conversely, under compressive stress applied parallel to the fiber direction, fissures manifest along the fiber orientation, leading to a notable reduction in compressive strength. Consequently, the primary contributory factor underlying augmented compressive strength is the lateral restraint effectuated by the fibers. The optimization of fiber distribution for the aim of altering compressive strength is subject to the influence of the qualities of the UHPC matrix. Moreover, a comprehensive analysis extends to the examination of pertinent parameters, encompassing fiber volume fractions, fiber lengths, and fiber shapes. Investigation of these facets reveals an optimal range of fiber volume fraction, approximately 1.0% to 1.5%, which imparts maximal compressive strength in ASF-UHPC subjected to compressive stress perpendicular to the fiber orientation. When forces are applied parallel to the fiber direction, the incorporation of longer fibers or hooked-end fibers mitigates the reduction in compressive strength perpendicular to the applied stress. The consideration of the transverse mechanical attributes exhibited by aligned steel fibers, coupled with the optimization of fiber distribution characteristics, not only attenuates steel fiber consumption but also underscores a sustainable approach by curtailing CO2 emissions.

Corrosive effect of HCl and H2SO4 exposure on the strength and microstructure of lithium slag geopolymer mortars

Resistance of geopolymer against aggressive effects of strong acid governs its service life. This research investigates the effect of silica fume incorporation on the strength degradation of lithium slag geopolymer (LSG) mortars after exposure to strong acids and presents the relationship between microstructure, calorimetry, and residual strength. Silica fume incorporated LSG mortars containing sodium (Na) and potassium (K) based alkaline activators were exposed to 5% sulphuric and hydrochloric acid solutions separately for 60 days. The sulphuric acid deterioration of LSG in terms of maximum percentage reduction in compressive strength was 37.42% upon incorporating 40% silica fume in geopolymer with a Na-based alkaline activator. LSG mixes activated by Na-activators demonstrated higher acid resistance compared to those activated by K-based activators. Leaching of aluminium (Al) from the aluminosilicate gel matrix occurred, which subsequently deteriorated aluminosilicate gel matrix when exposed to hydrochloric acid, whereas the leaching of Al occurs alongside the crystallization of calcium sulfate when specimens were exposed to sulphuric acid solution. The incorporation of silica fume reduces the initial calorimetric heat evolution and higher degree of geopolymerization marked by higher heat evolution between 5–48 h than the control LSG. The intense evolution of heat in control LSG at the initial stage of geopolymerization yielded a poor microstructure. Thus, acid-induced strength degradation is lower in silica fume-incorporated gel due to its denser microstructure and higher quantity of aluminosilicate gel formation. Hence, the incorporation of silica fume significantly improved its acid resistance, thus LSG may have industrial applications concerning acid exposure.

Evaluating the physicochemical properties of pervious recycled aggregate concrete incorporating pozzolanic additives under acid rain attack

The utilization of recycled concrete aggregate (RCA) from construction and demolition wastes to produce pervious concrete show various environmental benefits in the construction of sponge city. However, its durability performance in an acid rain attack environment has received less attention. This study aims to understand the deterioration of mechanical properties and microstructure of pervious recycled aggregate concrete (PRAC) exposed to simulated acid rain attack and drying-wetting cycles. The effects of the ground granulated blast-furnace slag (GGBS) replacement ratios, the silica fume (SF) replacement ratios and the erosion times on the mass loss, compressive strength, relative dynamic elastic modulus, permeability coefficient and porosity of PRAC were evaluated. The results demonstrated that the acid rain attack caused obvious mass loss and compressive strength reduction for PRAC without pozzolanic additives, thus resulted in increase on the permeability coefficient and porosity. Moreover, the physicochemical properties of PRAC decreased strongly with the increase of acid rain exposure time. Nevertheless, the addition of 20%GGBF and 7%SF in PRAC showed better resistance to acid attack due to the synergistic effect. The microscopic characterization revealed that the added pozzolanic additives declined the content of calcium hydroxide of matrix in PRAC and thereby inhibited the formation of gypsum, which delayed the acid rain erosion process.

Mechanical investigations of the durability performance of sustainable self-compacting and anti-spalling composite mortars

The durability of the mortar has recently been a critical concern, as it inherently contributes to the overall sustainability and resilience of the structure. This paper aims to address the growing demand for sustainable and durable infrastructure by investigating the effect of incorporating polypropylene, nylon, and jute fibers into self-compacting mortars. The performance of the mortar was tested under high temperatures, chemical attacks (Acid and sulfate attack), and freeze-thaw cycles. The mechanical properties were also examined through strength tests including compressive and flexural strength. Transport properties of mortars were investigated by water absorption, porosity, and sorptivity tests. Seven test mortar mixes were prepared, one of which was a control sample and six had polypropylene, nylon, jute fibers, and an entraining agent. Three of the six mortar mixes had 0.5 % polypropylene, nylon, and jute fibers while the other three had 1 % of these fibers. The effect of acid and sulfate was investigated by parameters of weight losses and reductions in compressive strength of mortar samples while the effect of freeze and thaw was investigated by comparing the drop in compressive strength of mortar specimens with and without fibers. The results revealed a drop in water absorption and porosity of mortar samples containing 0.5 % test fibers as than the control sample, while a slight increase was observed in water absorption and porosity for mortar samples incorporating 1 % of these fibers. The sorptivity of test samples was less than that of the control sample. The compressive strength of mortar samples having 0.5 % fibers was found to have increased, however, a slight reduction was observed in the compressive strength for samples having 1 % of these fibers. The addition of Polypropylene, Nylon, and Jute fibers significantly increased the flexural strength of mortar samples. There were lesser weight losses and compressive strength losses for mortar samples containing Polypropylene, Jute, and Nylon fibers as compared to the control mortar sample when subjected to 5 % HCL, 5 % sodium sulfate, and 28 freeze-thaw cycles. The addition of Polypropylene, Jute, and Nylon fibers has improved the durability performance of self-compacting concrete against different deteriorating phenomena, which eventually can result in durable and sustainable infrastructure.

Electric field-induced deterioration of cement mortars owing to calcium leaching

This paper investigated the calcium leaching from plain and fly ash/limestone blended cement mortars under an electric field. The Ca2+ leaching degree and reduced CaO content were measured to assess the extent of calcium leaching, and the compressive strength loss was used as an indicator to evaluate the degradation of the mortars due to leaching. Additionally, the changes in mineralogical composition, micrograph, Ca/Si ratio of C–S–H gel, and pore structure of leached samples were analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS), and mercury intrusion porosimetry (MIP). The findings indicated a notable acceleration in the leaching of Ca2+ due to the application of an electric field. Consequently, the calcium leaching degree of mortars continuously increased with time. The accelerated calcium leaching resulted in the loose microstructure and increased porosity mainly for the cathode part as well as the reduction in compressive strength of mortars. The addition of fly ash was beneficial in reducing the calcium leaching and strength loss of mortars after 90 days of exposure to the electric field, contrary to the effects observed with the incorporation of limestone powders. Attention should be paid to the durability issues of cement-based materials induced by the electric field.

Enhancing concrete performance: Surface modification of recycled coarse aggregates for sustainable construction

In this study, the researchers introduce an innovative method to enhance the utilization of recycled coarse aggregates (RCA) derived from construction and demolition waste (C&D) in sustainable concrete production. The presence of old cements mortar on the surface of these aggregates poses a challenge to their mechanical properties. To tackle this issue, the researchers propose a unique approach that combines chemical treatment and abrasion techniques. Firstly, RCA is immersed in a 0.5 mol hydrochloric acid (HCl) solution, weakening the adhering mortar. Subsequently, abrasion treatment removes the weakened mortar from the RCA surface. The study explores the incorporation of these surface-modified RCAs at varying levels, from 0% to 100% in 25% increments. Various concrete properties, including workability, compressive strength, flexural strength, split tensile strength, and microstructural characteristics (XRD, SEM, and EDAX), along with modulus of elasticity, are assessed. Results indicate that the combination of these modification techniques significantly enhances RCA properties. At the 100% replacement level, surface-modified RCA results in a reduction of compressive, flexural, and split tensile strength by 08.31%, 10.61%, and 07.90%, respectively, in comparison to the reference concrete. Likewise, the modulus of elasticity decreases to 30.82, and porosity decreases to 27.82% at the same replacement level. However, SEM analysis illustrates improved bonding between RCA and cement matrix due to surface modifications, leading to reduced porosity and the formation of dense Interfacial Transition Zones (ITZs). Cost analysis reveals that recycled aggregate concrete (RAC) mixtures can be more economical than those utilizing natural aggregates (NA). In summary, this novel surface modification technique presents a promising avenue for optimizing RCA utilization in sustainable concrete production, promoting environmental conservation, and efficient waste management in the construction sector.

Multi-scale failure mechanisms of hydraulic engineering exposed to seasonally frozen salinization environment: Integrating SBAS-InSAR and mechanical experiments

Constructing hydraulic engineering ensures agricultural development and improves salinization environments. However, in seasonally frozen salinization regions, hydraulic engineering is prone to deformation failure. Leakage from canal raises the regional groundwater level, triggering secondary salinization environmental issues. Exploring the instability mechanisms is thus necessary for hydraulic engineering. Traditional deformation monitoring techniques and soil experiments are constrained by observation scale and timeliness. In this study, Sentinel-1B data from November 2017 to August 2019 were acquired. The small baseline subset (SBAS) InSAR approach was employed to interpret the seasonal deformation characteristics in both the vertical and slope directions of a damaged canal segment in Songyuan, Northeast China. The mechanical properties of saline-alkali soil under varying water contents were quantified by integrating unconfined compression experiment (UCE). In May, as the soil thawed downward, a frozen lenses with poor permeability formed at a depth of approximately 100 cm, causing the accumulation of meltwater and infiltrated precipitation between the frozen layer and the melting layer in the canal. The soil water content at a depth of 80 to 140 cm exceeded 22 %, reaching a threshold for rapid reduction in unconfined compression strength (UCS). Consequently, in spring, the low soil strength between the frozen layer and the melting layer resulted in interface sliding, with a displacement of −133.88 mm in the canal slope direction. Furthermore, the differential projection of freeze-thaw deformation in the slope direction caused continuous creep of the canal towards the free face, with a value of −23.27 mm, exacerbating the formation of the late spring landslide. Integrating InSAR and engineering geological analysis is beneficial for addressing deformation issues in hydraulic engineering. Ensuring the sustainable operation of hydraulic engineering holds important implications for mitigating the salinization process.

LVI and CAI Analysis of Woven Carbon Fiber Reinforced Composite Laminates with Different Stacking Sequence

The study investigates LVI testing on woven carbon fiber-reinforced composite laminates at three different energy levels and assesses the specimens for their compressive strengths. X-ray CT scans are used to study the damaged envelopes, which allows better insights into the damage progression and failure mechanisms of the composite. The study investigates how post-impact damage propagation is influenced by alterations in impact energy and stacking orientation. The findings demonstrated that several variables, such as the characteristics of the constituent materials, the stacking order, laminate thickness, and ply orientations, had an impact on the CAI strength of the composite laminate. These findings highlight the importance of considering multiple factors when designing composite materials that can withstand impact loading and maintain their structural integrity. Even in specimens showing barely perceptible surface damage, a considerable drop in compressive strength is seen after the LVI testing. When specimens are struck with 25 J of energy, the compressive strength reduction reached a maximum value of 15.68%. In CAI testing, it is typical for sub-laminates to buckle near the impact-induced damage zone, resulting in failure. The magnitude of impact damage area can significantly affect the CAI strength, as the damaged area may create a stress concentration that can lead to buckling or other types of failure. Therefore, it is important to consider the impact energy and damage size when evaluating the CAI strength of composite materials.

Effects of Recycled Expanded Polystyrene Beads on the Mechanical and Physical Properties of Cement-Stabilized Compressed Earth Bricks

Nowadays, research on environmentally friendly materials has become a significant challenge in the field of civil engineering. In this study, stabilized compressed earth bricks (CEBs) incorporating recycled expanded polystyrene (EPS) beads were studied with the aim of enhancing the development of green constructions. The mass contents of recycled EPS in CEB formulated at a compaction pressure of 5 MPa are 0%, 0.25%, 0.5%, 0.75%, and 1% relative to the mass of the soil, while cement type CEM I 32.5, as a stabilizer, constituted 8% by mass. Characterization was carried out by determining densities, dry and wet compressive strength, flexural strength, total water absorption, and capillarity. Sample properties were found to be strongly influenced by the percentage of recycled EPS. Increasing the EPS aggregate content led to a reduction in compressive strength in both wet and dry conditions. Samples with 0.5% EPS and 8% cement offered better physical and mechanical performance. Samples containing EPS had relatively low water absorption, which would contribute to good durability. These CEBs comply with the wall construction requirements for two-story dwellings. This study also demonstrates the potential use of this recycled material in the construction industry.

Compressive Strength of RAC Cylinders Cast with Recycled Aggregates from Different Structural Members

In this research study, the effect on the compressive strength of recycled aggregate members is presented. Demolished waste was collected from five different structural members. Hammering was used to reduce the aggregate size to a maximum of 1 inch. Using a 1:2:4 mix and 0.5 w/c ratio, 55 cylinders in 11 batches were prepared for each source of coarse aggregates. Additionally, one batch of cylinders was prepared with conventional concrete and its results were compared with the others. Altogether, 280 cylinders of standard size were prepared and cured for 28 days. The compressive strength of all specimens was determined in a universal testing machine. The optimum replacement percentage with the least reduction in compressive strength was found to be 35%. Column concrete contributed most to compressive strength with a reduction equal to 6.23%, whereas beam concrete caused a 6.9% reduction. Further, a comparison for mixed aggregates by taking the average of all sources was conducted. It showed that 35% replacement was also the optimum with a reduction in strength equal to 8.63%.

Simple way to model the mechanical properties of concretes with recycled concrete aggregates

Researchers have made efforts to model the mechanical properties of concretes with recycled aggregates joining large research databases. The replacement ratio criterion of natural aggregates by recycled ones has been widely used in the models, however, itself leads to a great dispersion of results and is inaccurate. In the manuscript, the weighted water absorption of both aggregates (coarse natural and recycled concrete one, Ww) and the effective water/cement ratio were used to easily predict accurately the porosity, compressive strength, and elastic modulus of the recycled concretes. For the modelling, a systematic review of the Brazilian studies from 1999 to 2020 was conducted compiling 169 concrete compositions and joined with 212 concrete mixes from international studies. A supplementary Excel file with the database and all existing correlations was provided. The 20%-replacement ratio limit of many standard codes for structural recycled concretes can be exceeded by using Ww < 5 % for structural concrete [40–60 MPa], or Ww < 8 % [25–40 MPa]. Aggregates with Ww > 8 % can be used for non-structural concretes, with little reduction in compressive strength in absolute terms (<5 MPa). The best %-replacement can be defined for each case, practical for concrete formulations in ready-mix companies.