Lower Compressive Strength Research Articles

Anisotropy characteristics of electrical conductivity and compressive strength of 3D carbon fiber/epoxy angle-interlock woven composites

Electrical and compressive performances are important in 3D carbon fiber/epoxy angle-interlock woven (AIW) composites for mechanical-electrical coupling behaviors. Here we investigate the electrical conductivity and compressive strength of.3D AIW composites both in in-plane and out-of plane. Four-probe method is conducted to measure the volume resistance along different directions. Damage evolution and failure modes are recorded with a high-speed camera during compressive test. Electrical conductivity and compressive strength exhibit obvious anisotropic characteristics due to fiber orientation and yarn waviness. The curved warp yarns result in the compromise of the X-direction conductivity by extending the current transmission length and increase of the Z-direction conductivity by forming more contact points to expand the current flow paths. Because of different yarn arrangements, the compressive failure mechanisms of 3D AIW composites in the X, Y and Z directions are buckling failure, double shear bands and indirect tensile failure, individually. Yarn undulation in the X-direction causes premature buckling and exhibits elastic-plastic nonlinear response, resulting in the lowest compressive strength and modulus. The 3D AIW composites have the lowest electrical conductivity and highest compressive strength in the Z-direction, which is suitable for high strength stress-sensing elements.

COMPRESSIVE STRENGTH OF Ca(OH)2 COMBINED WITH MUSA ACUMINATA AS A PULP CAPPING MATERIAL

Background: The weakness of Ca(OH)2 is its low compressive strength and mechanical properties which can affect the stability of the material to the liquid in the tooth root canal so that it can dissolve the root canal medicament material. Due to the various weaknesses of Ca(OH)2, the researchers are interested in combining Ca(OH)2 with natural ingredients extracted from Musa acuminata (Mauli Banana) stem. Musa acuminata stem extract (MaSE) contains bioactive compounds such as tannins, saponins, alkaloids, flavonoids and lycopene which have antioxidant, anti-inflammatory, antibacterial and anti-viral properties. One of the requirements for pulp capping material is to have sufficient compressive strength, therefore, it is necessary to conduct research to test the value of the compressive strength of the combination of Ca(OH)2 with Musa acuminata stem extract. Purpose: To analyze the compressive strength of the pulp capping material from the combination of calcium hydroxide and Musa acuminata stem extract, with a ratio of 1:1; 1:1.5 ; and 1.5:1. Method: This research is a pure experimental study with a posttest-only design with a control group design, consisting of 4 treatment groups, including: group 1 the combination of Ca(OH)2 with Musa acuminata stem extract at 1:1, group 2 1:1.5, group 3 1.5:1, and group 4 as a positive control. Results: One Way Anova test (p<0.05) which means there is a significant difference. Data analysis was continued with the LSD Post Hoc test (p<0.05) which showed that there were significant differences between groups, between each treatment group. Conclusion: The combination of Ca(OH)2 with 50% MaSE and PG ratio of 1.5 : 1 : 0.375, has the highest compressive strength (1.40 MPa), so it can be concluded that the more Musa acuminata stem extract in the combination, the lower the compressive strength. Keywords : Calcium hydroxide, Compressive strength, Musa acuminata stem extract

Limitations and modifications in the clinical application of calcium sulfate.

Calcium sulfate and calcium sulfate-based biomaterials have been widely used in non-load-bearing bone defects for hundreds of years due to their superior biocompatibility, biodegradability, and non-toxicity. However, lower compressive strength and rapid degradation rate are the main limitations in clinical applications. Excessive absorption causes a sharp increase in sulfate ion and calcium ion concentrations around the bone defect site, resulting in delayed wound healing and hypercalcemia. In addition, the space between calcium sulfate and the host bone, resulting from excessively rapid absorption, has adverse effects on bone healing or fusion techniques. This issue has been recognized and addressed. The lack of sufficient mechanical strength makes it challenging to use calcium sulfate and calcium sulfate-based biomaterials in load-bearing areas. To overcome these defects, the introduction of various inorganic additives, such as calcium carbonate, calcium phosphate, and calcium silicate, into calcium sulfate is an effective measure. Inorganic materials with different physical and chemical properties can greatly improve the properties of calcium sulfate composites. For example, the hydrolysis products of calcium carbonate are alkaline substances that can buffer the acidic environment caused by the degradation of calcium sulfate; calcium phosphate has poor degradation, which can effectively avoid the excessive absorption of calcium sulfate; and calcium silicate can promote the compressive strength and stimulate new bone formation. The purpose of this review is to review the poor properties of calcium sulfate and its complications in clinical application and to explore the effect of various inorganic additives on the physicochemical properties and biological properties of calcium sulfate.

Research of the Component Composition of Drying Renovation Brick Crumb Plaster for Restoration of Architectural Monuments

The article presents the results of analytical studies to establish the authentic component composition of the brick crumb plaster, which was used to furnish architectural monuments of the 10th – 12th centuries. In laboratory conditions, a number of experimental studies aimed at the production of brick crumb plaster according to the historical recipe were performed. However, a number of requirements were set for such plaster, according to which it must meet European and domestic requirements for drying renovation plasters. The peculiarity of such plasters is low compressive strength (1.5 – 5.0MPa), high porosity (>45 %) and a low coefficient of resistance to water vapour diffusion (12), which allows drying overmoistened walls and at the same time extracting salts from them and accumulating them in the pores of their volume. In the process of experimental research, the historical recipe of the plaster was slightly modified, which made it possible to obtain a plaster with the specified parameters. The performance of plastering works with a scientifically based recipe of brick crumb renovation plaster on an architectural monument in the city of Chernihiv gave a positive result with a decrease in salinity and humidity of the walls.

Effect of variations in concrete quality on the crack width in rigid pavement

Cracks pose a significant issue in rigid pavement, leading to substantial damage. The manual mixing and casting of road pavement concrete underscore the importance of concrete quality as a critical parameter. This study investigates crack behavior by varying concrete quality. Loading is performed statically using line loads, shedding light on the impact of concrete quality on crack development. The concrete to be used has a quality fc' of 15 MPa, 25 MPa, and 35 MPa. The fine aggregate used in this study was Lumajang black sand, while the coarse aggregate used was machine crushed stone, and Portland Composite Cement (PCC) was used in all concrete mixes. The reinforcing steel used had a quality fy of 480 MPa, with a reinforcement ratio of ρ=0.010, which was converted to 5-D16 reinforcement. The subgrade density used to support the specimens had a CBR value of 10 %. Specimen dimensions were 2×0.6×0.2 m for length, width, and thickness. Pavement plates, 30 cm thick, were placed on leveled subgrade soil in a steel box set to achieve a 6 % CBR reading. Hydraulic jacks, monitored by a load cell, applied monotonic static loading with 2 kN intervals, reaching a maximum load of 200 kN. Steel tension and plate settlement were measured using a tension sensor and Linear Variable Differential Transformer (LVDT), respectively. A data logger recorded readings, and crack widths were captured by a digital microscope with 0.01 mm accuracy. Experimental results show that low concrete compressive strength values result in larger crack widths, and vice versa. Cracks also occur at earlier loading of concrete quality fc' 15 MPa. In addition, experiments show that the reinforcement stress value has a significant influence on crack width in specimens with low concrete quality

Investigation of Mechanical and Shrinkage Performance for Large-Size Cement-Stabilized Aggregates.

Cement-stabilized macadam materials are widely utilized as semi-rigid base materials in road construction. However, conventional cement-stabilized macadam (CCSM) bases often develop shrinkage cracks during early construction and maintenance due to variations in humidity and temperature. Shrinkage cracks can subsequently result in reflective cracks in the asphalt pavement, significantly reducing the overall service life of the road. This study systematically evaluates the shrinkage and mechanical properties of large-size cement-stabilized macadam (LSCSM). Initially, the mix proportion for LSCSM is determined using the Bailey method. Subsequently, an experimental design based on the response surface method is implemented to comprehensively investigate various properties, including unconfined compressive strength, compressive rebound modulus, flexural strength, and the durability aspects of early drying shrinkage and temperature shrinkage through laboratory experiments. Further, the performance differences between CCSM and LSCSM are analyzed comparatively. The findings reveal that the compressive strength of LSCSM surpasses that of CCSM, albeit with comparatively lower compressive rebound modulus and flexural strength. LSCSM demonstrates a unique blend of characteristics, exhibiting traits of both semi-rigid and flexible materials. Furthermore, LSCSM exhibits favorable crack resistance properties, as evidenced by lower dry shrinkage strain, average dry and temperature shrinkage coefficient compared to CCSM. The proposed LSCSM in this study effectively reduces cement dosage and enhances the crack resistance performance of base materials.

Analysis of pore structure characteristics of MSWI bottom ash micro powder concrete

Municipal solid waste incineration (MSWI) bottom ash is a type of bulk waste. Its potential activity can be better harnessed after it is ground into a fine powder, leading to reduced carbon emissions. This paper investigates the pore structure of MSWI bottom ash micro powder concrete and its impact on mechanical properties. Standard tests were conducted to evaluate the mechanical properties of MSWI bottom ash micro powder concrete with four blending ratios under three water-binder ratios. Subsequently, a mercury intrusion test was performed to determine its internal pore structure characteristic parameters. Remaining specimens from the macroscopic test were sampled, and concrete specimens were observed using a high-power electronic environmental scanning microscope to analyze morphological characteristics at various multiples and curing ages. The results indicate that the pore structure of MSWI bottom ash micro powder concrete is uniformly distributed, displaying good fractal characteristics conducive to subsequent secondary hydration reactions. The inclusion of MSWI bottom ash micro powder increases concrete porosity, leading to a decrease in compressive strength. However, as the curing age increases, the value tends to approach that of ordinary concrete, suggesting that MSWI bottom ash micro powder exhibits potential hydraulicity, albeit with a slow hydration reaction. The observed pattern of MSWI bottom ash micro powder concrete aligns with that of ordinary concrete, wherein higher porosity corresponds to lower compressive strength. The addition of MSWI bottom ash micro powder increases concrete porosity, resulting in reduced compressive strength.

The Effect of The Addition of Bagasse Ash on The Making of Paving Block

Paving Concrete is a composite of building materials made from a mixture of Portland cement or adhesive, water, and aggregate with or without other additives, which do not reduce the quality of the Concrete. In the research, fc' K-175 kg/cm2 of bagasse ash was added with variations of 0%, 6%, 8%, and 12% bagasse ash; the weight is based on the weight of the cement. This study aimed to determine the compressive strength of Concrete obtained from a mixture of bagasse ash in K-175 kg/cm2. The concrete mix design refers to SNI-03-0691-1996. Test samples prepared for each additional percentage of bagasse ash were three samples in the form of cubes with a length of 20 cm, a height of 8 cm, and a width of 10 cm. The results showed a decrease in strength with each addition of bagasse ash. It is known that the average compressive strength of Concrete after 28 days is 176.66%. Kg/m2 and the lowest compressive strength were obtained by adding 12% ash from bagasse aged 28 days, which was 73.33 kg/m2.

Role of process control agent in the production of Al2O3-reinforced titanium matrix composites

Metal Matrix Composites (MMCs) have recently been preferred over traditional materials in many engineering applications. Titanium matrix composites (TMCs) are used in the automotive, aerospace and defence industries thanks to their exceptional strength, high fatigue strength, good corrosion resistance and high elastic modulus. Some of the most used reinforcement materials for TMCs are SiC, Zr2O3, Al2O3, graphene, carbon nanotube (CNT) and TiC. In this study, TMCs reinforced Al2O3 were produced via conventional powder metallurgy (PM) and ultrasonic-assisted mixing. An Al2O3 in varying amounts (5 and 10 wt%) was incorporated into the TMCs via mechanical alloying (MA) for 5 h in a high-energy ball mill and using different process control agents (PCA, Stearic acid (SA), Polyvinyl Alcohol (PVA), Ethanol). The mechanically alloyed (MA'ed) powders were compacted by a hydraulic press under uniaxial pressure of 450 MPa and sintered at 1200 °C for 2 h in an argon atmosphere. The microstructural, mechanical and tribological properties of Ti-xAl2O3 powders and bulk samples were investigated. The highest hardness and the lowest specific wear rate were found in specimens reinforced with 5 wt% Al2O3, using ethanol as PCA, and produced by ultrasonic-assisted mixing, but the same specimen had the lowest compressive strength.

The Performance and Reaction Mechanism of Untreated Steel Slag Used as a Microexpanding Agent in Fly Ash-Based Geopolymers

Steel slag is an industrial by-product of the steelmaking process, which is under-utilized and of low value due to its characteristics. Alkali-activated technology offers the possibility of high utilization and increased value of steel slag. A geopolymer composition was composed of steel slag, fly ash, and calcium hydroxide. Four experimental groups utilizing steel slag to substitute fly ash are established based on varying replacement levels: 35%, 40%, 45%, and 50% by mass. The final samples were characterized by compressive strength tests, and Fourier-transform infrared spectroscopy measurements, thermogravimetric measurements, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, and mercury intrusion porosimetry were used to investigate the chemical composition and microstructure of the final products. Higher steel slag/fly ash ratios lead to a lower bulk density and lower compressive strength. The compressive strength ranges from 3.7 MPa to 5.6 MPa, and the bulk density ranges from 0.85 g/cm3 to 1.13 g/cm3. Microstructural and energy-dispersive X-ray spectroscopy analyses show that the final geopolymer products were a type of composite consisting of both calcium aluminate silicate hydrate and sodium aluminate silicate hydrate, with the unreacted crystalline phases acting as fillers.

Mechanical, bioactive, and long-lasting antibacterial properties of a Ti scaffold with gradient pores releasing iodine ions

The ideal bone implant would effectively prevent aseptic as well as septic loosening by minimizing stress shielding, maximizing bone ingrowth, and preventing implant-associated infections. Here, a novel gradient-pore-size titanium scaffold was designed and manufactured to address these requirements. The scaffold features a larger pore size (900 μm) on the top surface, gradually decreasing to small sizes (600 μm to 300 μm) towards the center, creating a gradient structure. To enhance its functionality, the additively manufactured scaffolds were biofunctionalized using simple chemical and heat treatments so as to incorporate calcium and iodine ions throughout the surface. This unique combination of varying pore sizes with a biofunctional surface provides highly desirable mechanical properties, bioactivity, and notably, long-lasting antibacterial activity. The target mechanical aspects, including low elastic modulus, high compression, compression-shear, and fatigue strength, were effectively achieved. Furthermore, the biofunctional surface exhibits remarkable in vitro bioactivity and potent antibacterial activity, even under conditions specifically altered to be favorable for bacterial growth. More importantly, the integration of small pores alongside larger ones ensures a sustained high release of iodine, resulting in antimicrobial activity that persisted for over three months, with full eradication of the bacteria. Taken together, this gradient structure exhibits obvious superiority in combining most of the desired properties, making it an ideal candidate for orthopedic and dental implant applications.

Factors Affecting Properties of Polymer Grouted Sands

The aim of this research was to undertake laboratory testing to investigate the beneficial effects of epoxy resin grouts on the physical and mechanical properties of sands with a wide range of granulometric characteristics. Six sands of different particle size and uniformity coefficients were grouted using epoxy resin solutions with three ratios of epoxy resin to water (3.0, 2.0 and 1.5). A set of unconfined compressive strength tests were conducted on the grouted samples at different curing periods and a set of long-term unconfined compressive creep tests in dry and wet conditions after 180 days of curing were also carried out in order to evaluate the development of the mechanical properties of the sands, as well as the impact of water on them. The findings of the investigation showed that epoxy resin resulted in appreciable strength values in the specimens, especially those of fine sands or well graded sands, grouted with the different epoxy resin grouts. Whilst the higher compressive strength and elastic modulus values at the age of 180 days were obtained for the finer sand, which ranged from 2.6 to 5.6 MPa and 216 to 430 MPa, respectively, the lower compressive strength and elastic modulus values were attained for the coarser sand with low values of the coefficient of uniformity, which varied from 0.68 to 2.2 MPa and 75 to 185 MPa, respectively. Moreover, all grouted sands showed stable long-term creep behaviour, with high values of the creep limit ranging from 67.5 to 80% of compressive strength. The presence of water had a negative marginal effect in the majority of the grouted specimens. In terms of physical properties, the permeability and porosity were estimated. The permeability of fine sands or well graded sands was decreased by two to four orders of magnitude. Using laboratory results and regression analysis, three mathematical equations were developed that relate each of the dependent variables of compressive strength, elastic modulus and coefficient of permeability to particular explanatory variables.

Evaluation of Compressive and Bending Strength of a Geopolymer Based on Lateritic Clays as an Alternative Hydraulic Binder.

In Bolivia, lateritic soils are common in humid tropical regions and can be used in the construction industry as an alternative to materials that cause a negative environmental impact, such as cement. The production of Portland cement causes environmental issues like significant greenhouse gas emissions and air pollution. To address this problem, geopolymers have been introduced as an alternative binder with low CO2 emissions. In this regard, geopolymers based on lateritic clays have been studied mineralogically, chemically, and on their compressive strength separately. However, there are still no studies on lateritic clays present in Bolivia and their mechanical, mineralogical, and chemical properties combined in a geopolymer. Therefore, this present research proposes the evaluation of a geopolymer made from laterite clays. Compression and flexural tests were carried out, along with mineralogical and chemical analyses on mortar and geopolymer cubes and prisms. The results indicate that the laterite clay-based geopolymer has lower compressive strength compared to Portland cement IP (cement type I with the addition of pozzolana) mortar. However, the flexural strength tests show a slight increase in the case of the geopolymer.

Influence of the coefficient of uniformity on bio-cemented sands: A microscale investigation

Microbially induced carbonate precipitation (MICP) is a bio-mediated ground improvement technique that can increase soil stiffness and produce cohesion within granular material. Most experimental investigations on MICP-treated soils are performed on idealized granular materials. Evaluating a narrow range of particle sizes dismisses the potential influence of soil fabric on MICP treatment efficiency. Therefore, little is known regarding the influence of soil fabric on the level of improvement achievable post-MICP treatment. We investigate the influence of the coefficient of uniformity (Cu) on the level of improvement that can be obtained from MICP treatment. This study couples unconfined compression testing with microscale observations obtained from x-ray computed tomography (CT) of two sand mixtures with different Cu values. A soil column and CT specimen of each sand mixture were prepared and received the same number of MICPinjections. The shear wave velocity (Vs) of the soil columns was monitored to evaluate the increase in soil stiffness over time. After MICP treatment, the bio-cemented columns were subjected to unconfined compressive strength testing. Results indicate that for a similar mass of carbonate, the soil with a larger Cu experienced a greater increase in Vs but a lower maximum unconfined compressive strength. Through CT imaging, the soil with a smaller Cu was observed to have a more uniform distribution of carbonate within the sand matrix whereas the soil with a larger Cu has more sporadic MICP trends. This study elucidates the influence of soil fabric on the level of improvement that can be achieved through MICP treatment and assesses the reliability of x-ray CT scanning of MICP-treated sands with moderate carbonate content.

Optimization of formulation ratios of geopolymer mortar based on metakaolin and biomass fly ash

This study investigated the factors affecting the properties of geopolymer (GP) mortars through a two-stage experimental program created through central composite design of experiments. Stage I focused on the effects of SiO₂/Al₂O₃, H₂O/Na₂O, and total water-to-total solids (W/S) ratios on mortars formulated using metakaolin (MK) as the only geopolymerization precursor, while Stage II evaluated the impact of introducing biomass fly ash (BFA) as a second precursor. Most importantly, the SiO₂/Al₂O₃ ratio was defined based on raw materials’ dissolution tests rather than on their starting chemical composition, setting this study apart from most published literature. The mortars’ properties of interest, taken as response variables, were the flow test spreading diameter, and the efflorescence level and compressive strength after 7 days of curing under ambient conditions. The results of Stage I, regarding GP mortars based on MK only, show that SiO₂/Al₂O₃, H₂O/Na₂O, and W/S all had a statistically significant effect on compressive strength. Regarding the efflorescence level, SiO₂/Al₂O₃ had the most significant effect, H₂O/Na₂O showed a small contribution, and W/S effect was not statistically significant. In stage II, the incorporation of BFA led to (MK + BFA)-based mortars with lower spreading diameter and compressive strength, and higher efflorescence levels, with % BFA being the most important factor affecting these three response variables. Based on the developed models, appropriate combinations of factor values that simultaneously maximize the compressive strength while maintaining the spreading diameter and efflorescence levels within suitable limits were found: GP mortars based only on MK with SiO₂/Al₂O₃ = 4.5, H₂O/Na₂O = 19.0, and W/S = 0.17 are expected to achieve 53MPa of compressive strength at 7 days; (MK + BFA)-based GP mortars with % BFA = 39.0, H₂O/Na₂O = 15.5, SiO₂/Al₂O₃ = 4.5 and W/S = 0.17 are expected to achieve 30MPa. These results provide valuable insights into the factors affecting the properties of GP mortars and can be useful for optimizing formulations for different applications.

Mechanical Response Analysis of Regular and Lightweight Concrete under Bending Stresses

This study investigated the mechanical response of regular and lightweight concrete under bending stresses. We compared the stress‐strain relationships, densities, and deformation capacities of these two types of concrete to highlight their key differences. Lightweight concrete, with a lower density of 1800 kg/m³, offers significant weight reductions, making it ideal for applications with weight constraints. However, this reduced weight results in lower compressive and flexural strengths. On the other hand, normal concrete, with a density of 2400 kg/m³, exhibited higher mechanical strength and durability. The stress‐strain graphs from the study showed that both concrete types exhibit both elastic and plastic deformation, with a transition from elastic to plastic behavior at specific stress points. By balancing weight reduction against mechanical strength, this study provides valuable insights for construction professionals in selecting the appropriate concrete type for various projects.

Fabrication and Compression Properties of Reinforced Epoxy Syntactic Foam With Basalt Fiber

Deep‐sea equipment is generally made of lightweight and pressure‐resistant materials in order to meet the requirements of the actual work. In order to explore marine resources better, it is necessary to research lightweight buoyancy materials for loading on mining equipment. These buoyancy materials contribute not only to providing adequate buoyancy to the mining equipment but also to reducing economic expenses. In this paper, hollow glass microspheres reinforced epoxy hollow spheres (HGMSs‐EHSs) were prepared by the rolling ball method using expanded polystyrene (EPS), epoxy resin (EP), and HGMS as raw materials. Epoxy syntactic foam (ESF) was manufactured by blending EP, curing agent, HGMS, and HGMS‐EHS with molding method. Basalt fiber (BF) reinforced ESF was fabricated by adding BFs to form a fiber network inside the syntactic foam. The results revealed that the density and compressive strength of ESF increased progressively with the number of HGMS‐EHS layers. The density and compressive strength of ESF decreased prospectively with the increase of the stacking volume fraction of HGMS‐EHS. The density and compressive strength of ESF increased gradually with the enlargement of the length and content of BF. In the range of influencing factors mentioned above, the density of ESF remains around 0.3 g/cm3, which has a low density. When the number of layers of HGMS‐EHS was two, the stacking volume fraction was 90%, the length of BF was 12 mm, the content of BF was 4%, the density of BF‐ESF was 0.316 g/cm3, and the compressive strength was 6.93 MPa. The compressive strength of prepared buoyancy material can meet the pressure resistance requirements for operations in waters of a certain depth. With a density of only 0.316 g/cm3, it provides sufficient buoyancy to balance the gravity of the equipment. Compared with the current study, in this paper, BFs were used as the reinforcing phase to prepare solid buoyancy foam with low density and high compressive strength. The experimental results demonstrate that this economical fiber material can effectively improve the compressive strength of buoyancy materials. This buoyancy material may be suitable for loading on small equipment for extracting marine resources. This work provides a reference for the preparation of low‐density solid buoyancy materials.

OPTIMIZATION OF CONCRETE CONTAINING SAWDUST ASH USING CENTRAL COMPOSITE DESIGN

Concrete admixed with materials with pozzolanic properties helps to reduce micro cracks which is the major problem faced by conventional concrete. Incorporating sawdust ash in concrete helps to produce sustainable and cost effective concrete structures. This investigation focused on partial replacement of cement with sawdust ash in concrete. The physical and chemical properties of sawdust used were extensively explored and characterised. The performance of concrete mixtures was assessed in terms of workability, tensile strength, flexural strength, water absorption. The durability of admixed concrete in acidic and sulphate environment was also assessed. Optimization was carried out using central composite design to generate optimal value and model equations for the responses. The preliminary study showed that sawdust ash had enough silica content which can help in strength development of concrete at later ages. The consistency of cement was 29% and increased with increasing sawdust ash content. From the results of numerical optimization, the optimum tensile strength of 2.69N/mm2 , flexural strength of 7.69 N/mm2 and water absorption of 1.33% were obtained at 10% SDA content and 56 days curing. It was evident that sawdust ash concrete absorbs more water compared to control specimens and also the strength of SDA concretes immersed in sulphate and acidic solutions have 50%MgSO4, 90%HNO3 23%Na2SO4 lower compressive strengths than the control cubes immersed in water only. The research recommends that research should be carried out to evaluate the effects of more supplementary locally available materials in binary and ternary mixture with SDA.

Investigation into the Mechanical Properties of Commercial Sandcrete Blocks Produced in Nigeria: A Case Study of Warri Metropolis

This study investigated the extent to which the mechanical strength of commercially produced sandcrete blocks in Delta State, Nigeria, conforms to recognized international standards. Fifty sandcrete blocks (28 curing days) were sampled from ten known sandcrete block manufacturers in Warri municipal area, five blocks from each manufacturer. The compressive strength of the blocks was determined in accordance with the American Society for Testing and Materials (ASTM) International guidelines. The results showed that the compressive strength of all the blocks failed to meet the Nigeria Industrial Standard (NIS) benchmark for load loading sandcrete block, while only 20% of the blocks attained NIS requirement for non-load bearing walls. Field observation revealed that poor mixing ratio of the sandcrete; inconsistencies in the batching method and sand used in the production of the sandcrete blocks were responsible for the poor quality (low compressive strength) of the sandcrete blocks manufactured in the region. The findings of this study underscore the importance for the Nigerian Institution of Structural Engineers, to rigorously monitor the strength of sandcrete blocks made in Nigeria to ensure that their quality meets internationally recognized standards. This will reduce the occurrence of structural damage in Nigeria, due to the use of low quality blocks for wall constriction.

Review of Residual Mechanical Properties of Concrete Mixed with Different Admixtures at High Temperatures

In this study, we analyzed results reported in existing literature to examine the residual mechanical properties of concrete mixed with different admixtures. Ground granulated blast furnace slag (GGBFS), fly ash (FA), and metakaolin (MK) were selected as admixtures for analysis, and data reporting the residual compressive strength of concrete with different admixtures at high temperatures were analyzed. Then, with reference to the ordinary Portland cement (OPC) using 100% cement, prediction formulas for the residual mechanical properties of concrete were derived for each selected admixture, and the resulting values were compared with the values of codes used in international concrete specifications. The residual mechanical properties of concrete showed different results depending on the admixtures used, and the concrete mixed with MK showed a higher compressive strength than OPC at room temperature compared with the values of the existing codes. With increasing temperature of concrete exposure, the trend of compressive strength showed convergence to the values of the existing codes. At room temperature, concrete mixed with GGBFS or FA showed a trend of similar or lower compressive strength compared with that of the existing codes; however, with increasing temperature, the residual compressive strength exceeded that of American Concrete Institute (ACI) and CEN codes. Thus, at room temperature, concrete mixed with MK had excellent compressive strength, but with increasing temperature, concrete mixed with FA or GGBFS was observed to exhibit superior residual mechanical properties.