28-day Age Research Articles

Impact of plastic waste fiber and treated construction demolition waste on the durability and sustainability of concrete

This study explores the mechanical and durability properties of Plastic-Fibre Reinforced Concrete, incorporating hand-shredded plastic fibers sourced from polyethylene bags and PET bottles. Evaluations, including compressive and split tensile strength tests, were conducted on M40 grade mixes containing plastic fibers and 100% treated Construction and Demolition Waste (CDW), comparing them with conventional concrete. The results demonstrate a significant enhancement in strength properties with the addition of 0.25%, 0.5%, 0.75%, and 1% plastic-fibres, alongside the complete replacement of coarse aggregate with CDW, particularly noticeable at both 7 and 28-day curing ages. Although higher fiber dosages led to a slight reduction in compressive by 7% at the optimum percentage of 0.25% of PE and 0.5% of PET, the flexural strengths and split tensile strength exhibited a proportional increase of 11.7% and 18%. Surface analysis via Scanning Electron Microscopy (SEM) and elemental composition determination using Energy Dispersive Spectroscopy (EDS) revealed minimal fiber damage post-exposure, confirming its efficiency and contribution to higher strength and reduced weight loss in optimum mix. This novel approach combines manually recycled plastic waste as fibers with treated CDW, enhancing concrete properties while promoting sustainability. Sustainability analysis indicates that utilizing 100% CDW and plastic fiber contributes to reduced energy consumption, lower carbon emissions, and economic benefits. These findings underscore the potential of integrating non-degradable plastics into concrete mixtures, combined with treated CDW, offering both environmental sustainability and enhanced performance advantages in construction materials.

3D printable earth-based alkali activated “ink”: Effect of alkali concentration and binder-to-aggregate ratio

This research attempts to investigate the effect of activator concentration (4 mol/L (M) and 8M) and binder-to-aggregate (B:A) ratio (ranging from 1:1 to 1:3 by weight) on extrudability and buildability of 3D printable natural earth-based alkali-activated materials (EAAM). It is found that natural clay in soil, used to replace 25 % of M-sand, imparts higher thixotropy, evident from 90 to 100 % recovery in viscosity compared to 65–80 % for corresponding control (containing only M-sand and no soil). Presence of clay increases the dynamic yield stress than control but reduces the plastic viscosity by 80 – 90 % in EAAM compared to corresponding control where interlocking between sand particles resists smooth extrusion of the material. EAAMs made with 8M NaOH have higher flow retention and maintain 95–100 % recovery in viscosity for longer duration than 4M EAAM. This contributes to superior extrusion quality of 8M EAAM than 4M EAAM. The findings suggest that binder content can be reduced as concentration of NaOH is increased from 4M to 8M. This is evident from lower layer deformation (0.09 % of original height) under self-weight and higher 3D printed buildable height of at least 457 mm in 8M EAAM with B:A of 1:2 compared to a maximum of 375 mm for 4M EAAM at higher B:A of 1:1. Ratios of wet compressive strength to dry compressive strength vary between 0.92 and 1.09 in 8M EAAM compared to 0.79 – 0.85 for 4M EAAM at 28-day age, suggesting lower sensitivity to moisture due to improved clay stabilization. Based on the strength and moisture sensitivity, the developed material can serve as a low-carbon and durable alternative to Portland cement in the construction of masonry elements in buildings, including cavity walls, panels, flooring tiles and façade members.

Time-Variant Chloride Ingress Models for Probabilistic Assessment of Concrete Bridge Decks with De-Icing Salt Attack

This study is to propose time-variant probabilistic models of surface chloride and diffusion coefficient based on the survey data of 16 concrete bridge decks with the attack of de-icing salts. These models are developed, because there is no study that simultaneously considers both time-variance and probabilistic descriptors in the model for concrete bridge decks. From the study, it can be found that long-term surface chloride and its time-variant development are fitted with Log-normal and Weibull distributions, respectively. In addition, the 28-day diffusion coefficient and age factor are fitted with Log-logistic and Triangular distributions, respectively. Considering only the mean value in the models, the corrosion-free residual life of concrete bridge decks is equal to 18.3 years based on the target value of critical chloride of 1.2 kg/m3, whereas their cracking-free residual life is equal to 29.5 years based on the target value of critical chloride of 2.0 kg/m3. In comparison with the probabilistic analysis, it was nevertheless found that at year 18.3, there are 38% and 20% probabilities to have rebar corrosion and concrete cracking, respectively. However, at year 29.5, there are 63% and 42% probabilities to have rebar corrosion and concrete. Specifically, there are 6 and almost 7 out of 16 bridge locations having rebar corrosion in the year 18.3 and concrete cracking in the year 29.5, respectively.

Mechanical properties and durability analysis of CS-CG stabilized soil: Towards sustainable subgrade soil enhancement

In this study, carbide slag (CS) and coal gangue (CG) powder were utilized to enhance the properties of the subgrade soil. CS-CG stabilized soil underwent lab experiments to assess its mechanical properties and durability. Tests included unconfined compressive strength (UCS), compressive resilient modulus (CRM), and California bearing ratio (CBR) at stabilizer dosages of 5 %, 10 %, and 15 %. Additional tests, such as dry-wet cycling, salt solution immersion, permeability, leaching, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP), were conducted specifically for the 10 % dosage. The mechanical properties and durability were comprehensively analyzed, with a microscopic investigation into pore size. Furthermore, the soil-water characteristic curve (SWCC) of CS-CG stabilized soil is derived through MIP, providing insights into its impact on the material's strength. Results showcased favorable bearing capacity and durability of CS-CG stabilized soil. The optimal mixing dosage is 10 %, with the best ratio being CS: CG= 70: 30. After 6 dry-wet cycles, UCS loss rate was 18.6 %, comparable to 4 % Portland cement (PC) stabilized soil. Dry-wet cycle characteristics surpassed PC and Lime stabilized soils. Immersion in a 5 % NaCl solution for 30 days yielded a UCS of 3.8 MPa at 28-day age, while exposure to 5 % Na2SO4 solution led to an 11.6 % strength decrease compared to NaCl. Permeability coefficient indicated low permeability akin to PC and Lime stabilized soils. Heavy metal content met standards, with minimal increase during cycles. Hydration products mainly comprised C-S-H gel, Ca(OH)2 crystals, and carbonate modification. Analysis suggested capillary and transition pores predominantly, with minimal macropores presence. Dry-wet cycles induced a marginal increase in pore size, with negligible overall impact. SWCC predicted water content (θs) ranged from 30 % to 32 %, with a slight increase in matrix suction during dry-wet cycles. CS-CG stabilized soil shows favorable mechanical properties, durability, and environmental sustainability, indicating its potential as a substitute for traditional cement and lime treatments in subgrade soil reinforcement.

Enhancing biofilm resistance and preserving optical translucency of 3D printed clear aligners through carboxybetaine-copolymer surface treatment

ObjectivesThis study aimed to use a carboxybetaine methacrylate (CBMA) copolymer solution to surface treat 3D printed clear aligners at different fabrication stages, to impart antifouling properties, and assess the surface treatment at various fabrication stages' impact on physico-mechanical characteristics. MethodsSurface treatments using a blend of 2-hydroxyethyl methacrylate (HEMA) and CBMA, termed CCS, were performed at various stages of 3D printed clear aligner fabrication. Experimental groups, CB1, CB2, and CB3, were determined by the stage of surface treatment during post-processing. CB1, CB2, and CB3 received treatment before post-curing, after post-curing, and after post-processing, respectively. Untreated samples served as controls. Physical and mechanical properties were assessed through tensile testing, Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and UV-Vis spectroscopy. The surface was further characterized through scanning electron microscopy and contact angle measurements. The cytotoxicity was assessed with 7-day elution and agar diffusion assays. Lastly, bacterial biofilm resistance was evaluated using confocal laser scanning microscopy. Crystal violet assay was performed using Streptococcus mutans. ResultsSurface treatment during CB1 stage exerted the most significantly unfavorable influence on properties of the 3D printed aligner resin. CB2 samples showed the maximum preservation of translucency even after 7-day aging. CB2 and CB3 phases showed enhanced hydrophilicity of sample surfaces with reduced adhesion of multispecies biofilm and S. mutans. SignificanceApplication of CCS surface treatment immediately after post-curing (CB2) can enhance the biofilm resistance of 3D printed clear aligners while maintaining high fidelity to optical translucency and constituent mechanical properties.

An Investigation of the Mechanical and Durability Properties of Hollow Concrete Blocks Made with Copper Mine Tailings as a Partial Cement Replacement

The increase in copper productivity in Zambia has resulted in the expansion of disposal areas occupied by mineral wastes and tailings. This not only consumes land but also, due to insufficient management, poses negative environmental impacts and health risks to people. Therefore, efficient and sustainable approaches for the proper management of these waste materials must be developed. In this study, the potential utilization of copper mine tailings was assessed. After analyzing the physical and chemical properties of copper mine tailings from Kitwe Tailings Dam (TD25), hollow concrete block specimens were prepared. Copper mine tailings were used as a partial replacement for cement in the mix design, with replacement ratios as follows: 0% for CBCMT O% (control specimen), 10% for CBCMT1O%, 20% for CBCMT2O%, 30% for CBCMT3O%, 40% for CBCMT4O%, and 50% for CBCMT5O%, all aimed at achieving a target strength of 5 MPa. Specimen compressive strength was evaluated, and it was found that CBCMT1O% and CBCMT2O% achieved the target compressive strength at 28 days of age. Water absorption rates and resistance to acid attack were also assessed. Findings revealed that all specimens outperformed the control specimen in terms of these properties. Furthermore, the environmental feasibility of the hollow concrete blocks specimens was examined, and the results showed limited leaching of heavy metals from the specimens, with concentrations within permissible thresholds. Additionally, a statistical analysis was conducted to study the influence cell shape has on the specimens’ compressive strength. Aimed at identifying the optimal specimen type for achieving compressive strength at an early age, results indicated that cell shape had a significant impact on the 28-day age of hollow concrete blocks. The study proposes a novel copper mine tailings (waste) management approach, by utilizing the potential it has to replace cement in the production of hollow concrete blocks, evident from the observed enhancement of the mechanical and durability properties.

Utilizing Edge-Oxidized Graphene Oxide to Enhance Cement Mortar's Properties Containing Crumb Rubber: Toward Achieving Sustainable Materials.

Scrap tires have become one of the most serious environmental issues worldwide in recent years. Exploiting this scrap has caught the attention of researchers in their efforts to conserve the environment. From a structural engineering materials perspective, a partial fine aggregate in cement mortar can be replaced by crumb rubber produced from scrap tires. This research mainly emphasizes the role of adding 0.1% edge-oxidized graphene oxide EOGO (by the weight of cement) in enhancing the properties of cement mortars containing 5%, 10%, and 15% of crumb rubber (by sand replacement). Cube and prism specimens were employed to investigate compressive and flexural strengths at 7- and 28-day curing ages. A porosity test was also conducted after 28 days of curing. In addition, a scanning electron microscopy (SEM) test was performed to investigate the effect of incorporating EOGO on the interfacial transition zone (ITZ). Results showed an enhancement of the mechanical properties of cement mortar, including compressive and flexural strengths, with the inclusion of EOGO in the mixes. The findings demonstrated that adding EOGO can improve the mechanical properties of mixes containing crumb rubber particles. Specifically, the mortar mix with 0.1% EOGO and 5% crumb rubber exhibited better performance compared with the virgin mix without rubber particles. Therefore, crumb rubber is viable for use as a sand replacement when EOGO is included.

The Influence of Peat Water on the Physical Properties of Underwater Concrete

Casting concrete underwater is concrete used for structural work underwater. The main problem in underwater casting is the separation of concrete constituent materials. Casting underwater also does not involve compaction. This study will examine the effect of peat water on the physical properties of underwater cast concrete. The additive used in this study is in liquid form, with a mixture of anti-washout material 1.8% and self-compacting concrete 5% to the weight of cement. The obtained slump flow value is 470 mm. The results of volume weight testing on variations of clean water mixtures immersed in clean water for seven days are 2248,14 kg/m3 and 2258,96 kg/m3 for 28 days, variations of clean water mixtures immersed in peat water for seven days are 2224,49 kg/m3 and 2219,39 kg/m3 for 28 days, and variations of peat water mixtures immersed in peat water for seven days are 2202,50 kg/m3 and 2191,08 kg/m3 for 28 days. The decrease in volume weight occurs in variations immersed in peat water. The results of porosity testing on 7-day and 28-day concrete age variations of peat water mixtures immersed in peat water are 9,94% and 10,78%, variations of clean water mixtures immersed in peat water are 9,84% and 10,28%, and variations of clean water mixtures immersed in clean water are 9,73% and 8,70%. The SEM test results show the surface shape of concrete using a magnification of 1000x, more pores on variations of peat water mixtures immersed in peat water, and variations of clean water mixtures immersed in peat water have uneven surfaces and pores. In contrast, variations of clean water mixtures immersed in clean water have better surfaces. The additive used can work well with peat water and clean water.

Mortality of elderly patients with acute kidney injury undergoing continuous renal replacement therapy: is age a risk factor?

Whether advanced age is associated with poor outcomes of elderly patients with acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT) is controversial. This study aimed to evaluate age effect and predictors for mortality in elderly AKI patients undergoing CRRT. Data of 480 elderly AKI patients who underwent CRRT were retrospectively analyzed. Subjects were stratified into two groups according to age: younger-old (age, 65-74 years; n = 205) and older-old (age, ≥75 years; n = 275). Predictors for 28-day and 90-day mortality and age effects were analyzed using multivariable Cox regression analysis and propensity score matching. Urine output at the start of CRRT (adjusted hazard ratio [aHR], 0.99; 95% confidence interval [CI], 0.99-1.00; p = 0.04), operation (aHR, 0.53; 95% CI, 0.30-0.93; p = 0.03), and use of an intra-aortic balloon pump (aHR, 3.60; 95% CI, 1.18-10.96; p = 0.02) were predictors for 28-day mortality. Ischemic heart disease (aHR, 1.74; 95% CI, 1.02-2.98; p = 0.04) and use of a ventilator (aHR, 0.56; 95% CI, 0.36-0.89; p = 0.01) were predictors for 90-day mortality. The older-old group did not exhibit a higher risk for 28- day or 90-day mortality than the younger-old group in multivariable or propensity score-matched models. Advanced age was not a risk factor for mortality among elderly AKI patients undergoing CRRT, suggesting that advanced age should not be considered for therapeutic decisions in critically ill elderly patients with AKI requiring CRRT.

The mechanical and frost resistance properties of pressed concrete blocks mixed with the polymeric aluminum chloride waste residue.

This study aims to research on the mechanical and frost resistance properties of pressed concrete blocks mixed with the polymeric aluminum chloride (PAC) waste residue. Experimental studies on the activity index of volcanic ash, mechanical property, frost resistance and microstructure of pressed concrete blocks mixed with PAC waste residue were carried out. The results show that the activity index of volcanic ash of PAC waste residue reaches 74.96% at a particle size of 0.075mm or less and a curing age of 28days. Based on results of mechanical property tests, the optimum dosage of PAC waste residue is 15%, at which time the compressive and bending strength only decreases by 14.57% and 15.84%. Based on results of frost resistance tests, the optimum dosage of PAC waste residue for pressed concrete blocks is 10%. After 50 freeze-thaw cycles, when the dosage of PAC waste residue is 10%, the strength loss rate is only 3.04%. XRD and SEM tests show that PAC waste residue participates in chemical reactions. With a small amount of PAC waste residue, the structure of the specimen remains dense and therefore the strength decreases less.

INFLUENCE OF FEED ADDITIVE "ENZAKTIVE MIX" ON THE HEMATOLOGICAL PROFILE OF THE BLOOD OF SOWS AND THEIR PIGLETS

The dynamics of the haematological profile changes and the productivity of sows and piglets obtained from them when feeding the feed additive "EnzActive Mix" were described in the article. The feed additive contains yeast of the genus Saccharomyces cerevisiae with an activity of at least 1.5 x 10^10 CFU/g and a six enzymes complex with protease, cellulase, xylanase, ɑ-amylase, β-gluconase, phytase, which are located under the layer of yeast cells. The results of the study showed that the use of "EnzActive Mix" in sows and their piglets’ diet has a stimulating effect on the oxygen transport function of blood. This is evidenced by a higher number of erythrocytes and platelets, a higher concentration of haemoglobin and haematocrit in the blood of sows of the experimental group compared to the control group on 21st day of lactation (p<0.05). Addition of the feed additive "EnzActive Mix" to the diet caused changes in certain forms of leukocytes ratio in the sows’ blood. Thus, during this period, a higher (p<0.05) relative lymphocytes number and a tendency to decrease of segmented neutrophils number in the blood of experimental group sows compared to the control group were found. Similar changes were noted in the haematological parameters study of piglets obtained from these sows. In particular, the leukocytes number in the blood of the experimental group piglets at 5-, 14- and 28-day age was higher than in their peers of the control group. At the same time, on the 5th day of life, the differences relatively to the control group animals were significant (p<0.05). Feeding of the feed additive led to a decrease in the segmented neutrophils relative number in the blood of the experimental group piglets on the 14th and 28th day of life (p<0.05) and an increase in the lymphocytes number (p<0.05) during the indicated periods of the study. The positive effect of the feed additive "EnzActive Mix" on the productivity parameters of the studied animals was established. In particular, the body weight of experimental group piglets at 5-, 14- and 28-day age was 7.8%, 13.7% (p<0.05) and 8.4% (p<0.01) higher, respectively, than that of the control group.

Study on Sorptivity Test on Fly Ash Aggregate Concrete

Aggregate is most widely used in reinforced concrete construction. In this investigation, fly ash aggregates were used in concrete and its effect on durability of concrete was studied. The fly ash was collected from Mettur Thermal Power plant. Then the cement fly ash proportion of 10:90, 12.5:87.5, 15:85, 17.5:82.5, 20:80 and 22.5:77.5 were adopted to get fly ash aggregates. The Particle size distribution, Specific gravity and Water absorption tests on aggregates were conducted. M20 grade of concrete was considered. The fresh concrete tests like Slump test and Compacting factor test were conducted. For the plain concrete and fly ash aggregate concrete the cubes were cast. All the specimens were cured in a curing tank. The plain and fly ash aggregate concrete cube specimens were cast and tested at the age of 28days and 56days. Sorptivity and saturated water absorption tests were conducted on these plain and fly ash aggregate concrete specimens. The results were tabulated and compared by drawing graphs. Based on the results obtained, conclusions and suggestions were made.

Depth of Interbreed Difference in Postmortem Bovine Muscle Determined by CE-FT/MS and LC-FT/MS Metabolomics.

Japanese Brown (JBR) cattle have moderately marbled beef compared to the highly marbled beef of Japanese Black (JBL) cattle; however, their skeletal muscle properties remain poorly characterized. To unveil interbreed metabolic differences over the previous results, we explored the metabolome network changes before and after postmortem 7-day aging in the trapezius muscle of the two cattle breeds by employing a deep and high-coverage metabolomics approach. Using both capillary electrophoresis (CE) and ultra-high-performance liquid chromatography (UHPLC)-Fourier transform mass spectrometry (FT/MS), we detected 522 and 384 annotated peaks, respectively, across all muscle samples. The CE-based results showed that the cattle were clearly separated by breed and postmortem age in multivariate analyses. The metabolism related to glutathione, glycolysis, vitamin K, taurine, and arachidonic acid was enriched with differentially abundant metabolites in aged muscles, in addition to amino acid (AA) metabolisms. The LC-based results showed that the levels of bile-acid-related metabolites, such as tauroursodeoxycholic acid (TUDCA), were high in fresh JBR muscle and that acylcarnitines were enriched in aged JBR muscle, compared to JBL muscle. Postmortem aging resulted in an increase in fatty acids and a decrease in acylcarnitine in the muscles of both cattle breeds. In addition, metabolite set enrichment analysis revealed that JBR muscle was distinctive in metabolisms related to pyruvate, glycerolipid, cardiolipin, and mitochondrial energy production, whereas the metabolisms related to phosphatidylethanolamine, nucleotide triphosphate, and AAs were characteristic of JBL. This suggests that the interbreed differences in postmortem trapezius muscle are associated with carnitine/acylcarnitine transport, β-oxidation, tricarboxylic acid cycle, and mitochondrial membrane stability, in addition to energy substrate and AA metabolisms. These interbreed differences may characterize beef quality traits such as the flavor intensity and oxidative stability.

Recycling of Egyptian Shammi Corn Stalks for Maintaining Sustainable Cement Industry: Scoring on Sustainable Development Goals

This study focuses on recycling Shammi corn stalks in the cement industries, further avoiding air and soil pollution caused by their improper disposal. This crop residue was thermally treated at 700 °C for 2 h under an oxygen-rich environment to produce Shammi corn stalk ash (SCSA). This SCSA was used as a cement replacement material (2–10%, w/w), whereas the control sample included only cement. The compressive strength values for the 4% (w/w) replacement ratio at 2-, 7-, and 28-day ages were greater than those for the control by 26.5%, 15.8%, and 11.4%, respectively. This 4% (w/w) also maintained a better flexural strength than other mixtures, with proper initial and final setting times (135 and 190 min), workability (18.5 cm), and water consistency (27.5%). These mechanical/physical properties were integrated with socio-enviro-economic data collected from experts through a pairwise comparison questionnaire, forming the inputs of a multi-criteria decision-making (MCDM) model. Recycling SCSA in the cement-manufacturing process attained positive scores in the achievement of the three pillars of sustainable development, revealing an overall score greater than the control. Hence, the study outcomes could be essential in developing green concrete, cement blocks, and mortar, based on the sustainable development goals (SDGs) agenda.

Development of 3D printable stabilized earth-based construction materials using excavated soil: Evaluation of fresh and hardened properties

Soil excavated during construction and demolition can be utilized to reduce the demand for natural sand in 3D printed constructions. This research attempts to systematically develop 3D printable stabilized earth-based materials using excavated soil (clay content of 42.5 %) as 25 % and 50 % replacement of natural sand, and examine their compressive strength, water permeable porosity, and moisture sensitivity. The effectiveness of two binder systems – Ordinary Portland Cement (OPC) and a combination of OPC and ground granulated blast furnace slag (GGBS used to replace 30 % OPC by mass), was investigated. Non-expansive clay in the soil leads to a steeper reduction in apparent viscosity, 12–15 % higher flow retention, and 50–60 % lower plastic viscosity of soil-based mixes, thus contributing to superior extrusion quality at 35–40 mm lower initial flow than OPC-sand and OPC-GGBS-sand mixes. The addition of GGBS, due to its irregular particle morphologies and interlocking effects, further enhances the shape retention of the printed layers by 8–26 % compared to OPC-soil mortars. The structural build-ups in OPC-soil and OPC-GGBS-soil mortars increase with the increase in clay content, which enabled buildability up to a height of 1.2 m compared to only 0.51–0.55 m for OPC-sand and OPC-GGBS-sand mortars. Higher water demand due to the addition of natural clay increases the porosity of 3D printed OPC-soil mortars, thereby lowering compressive strength and increasing moisture sensitivity. However, a blend of OPC and GGBS substantially reduces the moisture sensitivity of the printed mortars at 28-day age, attributed to better stabilization of clay through hydraulic and pozzolanic action of GGBS. 28-day wet compressive strength of 14–25 MPa is obtained for the printed soil-based mixes depending on the soil dosage and loading direction. In summary, the study provides a feasible solution for the 3D printing of stabilized earth structures with lower demand for natural sand and OPC.

Strength Performance of Concrete Containing Rice Husk Ash as Cement Replacement in Presence of Polypropylene Fiber

This study focuses on the utilization of Rice Husk Ash (RHA) as partial replacement of Ordinary Portland Cement (OPC) in concrete in addition with Polypropylene (PP) fiber. The main goal of this study was to decrease dependence on OPC and address environmental waste generated through rice mills. This study considered concrete cubes prepared through 1:2:4 ration with 0.50 water-cement ratio with and without RHA and PP fibers. The water curing was done for 7 and 28 days, with three specimens for each proportion, and the average value was considered as the result. It was observed that the compressive strength of M2 concrete which containing 10% RHA was noticed 7% higher than the control mix concrete and declared as 10% RHA as optimum dosage. Next, the performance in terms of compressive strength of concrete containing optimum dosage of RHA in presence of PP fibers of three different lengths were also evaluated and found that the 0.1% of PP fiber of 0.5 inches length gives the 25% higher strength performance as compared to the control mix and 17% higher than the concrete containing 10% RHA only at the age of 28days. Hence, this study concluded that the replacing OPC cement with 10% RHA produces satisfactory strength performance and incorporation of PP fiber gives better strength performances.

Carbon dioxide sequestration in mortars with excavated soil: Engineering performances and environmental benefits

Globally, substantial volume of excavated soils is generated during construction and demolition activities, which can be utilized in the manufacturing stabilized earth-based construction materials. Furthermore, increasing amount of CO2 is being released into the environment from growing industrial operations that can sequestered in earth-based materials without compromising the engineering properties. This article attempts to explore the effect of CO2 sequestration through accelerated carbonation curing on engineering properties, micro-structure and phase composition of cement-lime stabilized soil mortars. Lateritic soil (clay content of 42 %) is used to replace 25 % and 50 % of natural sand by mass. The experimental findings demonstrate an increase in CO2 uptake by 15–23 % and 33–40 % due to addition of 25 % and 50 % soil respectively compared to control (0 % soil). Precipitation of meta-stable calcium carbonates majorly contributes to the total CO2 uptake, accounting for 62–69 % and 78–87 % of the carbonates formed in 25 % soil-mortars and 50 % soil mortars. These are substantially higher compared to 40–50 % in the case of control mixes. The mentioned finding is attributed to the formation of additional calcium-silicate-hydrate and calcium-aluminate-hydrate due to clay-lime reaction, that binds CO2 and precipitate meta-stable polymorphs of calcium carbonate. Addition of lime and carbon sequestration are found to substantially enhance 1-day strength of cement-soil and cement-lime-soil mortars by 31–36 %, although no prominent effect at 7-day and 28-day marks are observed. Furthermore, capillary water absorption at 28-day age is reduced by 18–31 % in lime-added cement-soil mortars compared to the ones without lime, that reduces moisture sensitivity of the mortars. Overall, the carbon sequestered mortars demonstrate satisfactory strength (20–37 MPa) and water absorption performance of the stabilized mortars for masonry applications, which will provide a promising means to manufacture low-carbon and more durable construction products.

Investigating the effects of ageing condition and type of aggregates on the properties of asphalt mixtures

In this study, asphalt mixtures made by steel slag (SSA), copper slag (CSA), limestone (LA) and siliceous (SA) aggregates were subjected to different aging conditions; and were evaluated using Marshall, indirect tensile strength (ITS), Cantabro abrasion loss and semi-circular bending (SCB) tests. Results reveal that the moisture damage, raveling and fracture resistance of asphalt mixture decrease with aging and the ITS and Marshall properties improve with aging. After 7-day long-term aging, the TSR of the mixtures made by LA, SA, SSA and CSA, decreases, 28.8%, 48.5%, 8.8% and 15%, respectively, while, the ITS in dry condition increases, 61.9%, 33%, 62% and 81%, respectively. The fracture properties and moisture damage resistance of asphalt concrete made by SSA and CSA are less affected by aging than those made by LA and SA. Statistical analysis revealed that the effect of aggregate type, aging condition and their interaction on the mixture properties is significant.

High activity pozzolan obtained from selection of excavation soils in a Construction and Demolition Waste landfill

Excavations soils from construction sites, when included as Construction and Demolition Waste (CDW) can double waste amount and represent up to 80 % of waste composition. Limited recycling strategies are available for the material. In this work, soils with higher kaolinite contents were selected by X-ray diffraction (XRD) to produce high activity pozzolan. Twenty soil samples were collected in an inert CDW landfill, and seven samples (one-third of the total) containing higher kaolinite content were composed as a single sample for thermal and mechanical activation as pozzolan. At the temperature of 600 °C, low crystallinity kaolinite was transformed into amorphous material (37 % g/g) achieving the highest pozzolanic activity [consumption of 519 mg Ca(OH)2/g of the sample]. The replacement of Portland cement by calcined soil (6, 10 and 18 %) had no significant rheological impact on the water to solid ratio and optimal dispersant content and affected slightly the heat and setting time of the pastes; therefore, workable, and technically applicable. The Portland cement replacement by calcined soil, despite a fixed water to solid ratio of 0.3 led to an increase in the water to cement ratios and in the porosities of the pastes. Due to the pozzolanic reaction, 6 and 10%-replacement of Portland cement by calcined soil did not impair the tensile strength of the pastes when compared to that of Portland cement paste. A 42-MPa 28-day age blended Portland with calcined soil might be feasible to produce regarding Brazilian cement industry standard.

Study on the Synergistic Effect of Superabsorbent Polymer and Crystalline Admixture on Self-Healing Performance of Mortar Based on Image Binarization Method

Concrete self-healing technology is an effective method for autonomously repairing cracks, which can reduce the maintenance costs of concrete components and prolong their service life. This study investigates the mechanical properties and self-healing abilities of mortar with internally mixed superabsorbent polymers (SAPs) and crystalline admixtures (CAs). The compressive strength and recovery rate of the specimens were evaluated, and the self-healing performance of concrete specimens was assessed through water absorption tests and optical microscopy observation of healed cracks. Microscopic analysis of the crack fillings was conducted using SEM-EDS and XRD tests, revealing the mechanism of the synergistic effect of SAPs and CAs on self-healing. The results indicate that the physical filling effect of SAPs’ water absorption and expansion almost completes the healing action before the 7-day healing age, with a weakened healing ability after this age. The chemical action of CA activation continues to heal cracks up to the 90-day healing age. When SAPs and CAs are incorporated together into the concrete matrix, the mortar specimens exhibit the best healing ability before the 7-day healing age. As water is released from the SAPs, the ongoing activation reaction of CAs shows the most effective healing result at the 90-day age. SEM-EDS analysis confirmed that the addition of CAs increases the Ca/Si ratio of calcium silicate hydrated, transforming it from an amorphous cluster structure to a needle-like structure. Furthermore, the internal curing effect of SAPs promotes the activation reaction of CAs, resulting in a greater quantity of more densely structured calcium silicate hydrated.