Permeability Of Concrete Research Articles

Effect of mixed basalt fiber and calcium sulfate whisker on chloride permeability of concrete

Rapid chloride migration (RCM) test was used to determine the non-steady-state chloride migration coefficient (DRCM) of concrete mixed with calcium sulfate whisker (CSW) and basalt fiber (BF). Meanwhile, the microscopic morphology of CSW and BF in concrete was observed through scanning electron microscope (SEM), and the microstructural parameters were determined by the nuclear magnetic resonance (NMR) method. Results show that mixes with 3.0 kg/m3 CSW or BF alone outperformed in terms of chloride penetration reduction. However, by considering the strength factors comprehensively, the effect of enhancing concrete strength and chloride permeability resistance is better when 3.0 kg/m3 CSW and 4.5 kg/m3 BF are mixed. Binary problem optimal analysis results show that the optimal admixture dosage for improving the chloride impermeability and the optimum admixture dosage for enhancing the compressive strength (fc) of concrete are not consistent. According to SEM results, CSW is evenly distributed in the matrix and BF is wrapped by concrete matrix. The addition of BF and CSW to concrete reduced its porosity according to NMR tests. Increasing the content of BF would increase the contributive porosity (φ) of macro pores in concrete, while CSW could reduce the φ of macro pores. The DRCM has the strongest correlation with φ with a pore size of 100–1000 nm, followed by porosity.

A functional and robust super‐hydrophobic PCC coating based on the induced assembly of modified zirconium phosphate

AbstractImproving the permeability of concrete is one of the important measures to extend the service life of concrete. In addition, for marine engineering, sewerage projects, and so on, mechanical stability and microbial induced corrosion of concrete structures cannot be ignored. We demonstrated a method to prepare high‐performance super‐hydrophobic (SHP) coating using functional zirconium phosphate (ZrP) and polydopamine (PDA) as the primary materials. The micro‐nano rough structures were constructed on the concrete surface by alternating organic–inorganic assembly guided by each other. The coatings' apparent morphology, composition, and structure were analyzed using various surface analysis techniques. Based on the construction of micro‐nano rough structures by the induced assembly of functional ZrP, the silane treatment significantly improved the water contact angle of the coating (WCA = 154° ± 3°), and the coating exhibited relatively high wear resistance, reaching 135° WCA even after 30 friction cycles. The water absorption of the specimens treated with the SHP composite coating was reduced by 79% to treated with silane. Meanwhile, the SHP composite coating showed excellent antimicrobial and anti‐ice properties, due to the role of the functional ZrP and alternating organic–inorganic assembly. It was expected that the composite coating might potentially promote and accelerate applied superhydrophobic anticorrosive coating development for marine concrete durability.

Effect of crystalline admixture on early‐age residual stress and cracking potential of high‐strength concrete

AbstractCrystalline admixture (CA) has been extensively utilized as the commercial product for improving the performance associated with strengthening self‐sealing of cracks or decreasing the permeability of concrete. However, few researches characterizing the restrained shrinkage and cracking potential of concrete with CA at early age. This paper aimed to expand the limitation by means of the experiments including mechanical properties test and restrained ring test on high‐strength concrete (HSC) with CA from Xypex. The proportion of CA was 0%, 0.5%, 1.0%, and 1.5% by the mass of cement. The incorporation of CA enhanced the compressive and splitting tensile strength as well as modulus of elasticity tested in this paper. A significant increase was observed in free and restrained shrinkage of HSC with CA. Although incorporation of CA ameliorated the stress relaxation, residual stress in restrained concrete ring developed rapidly with the incorporation of CA due to the significant increase in restrained shrinkage at early age. Restrained concrete ring with CA demonstrated a higher stress rate, which implied a higher cracking potential. When CA proportion increased from 0% to 0.5%, 1.0%, and 1.5%, a higher cracking potential was revealed through calculation, and restrained concrete ring exhibited earlier cracking age. Caution should be exercised with the application of such CA in concrete mixtures under restrained conditions.

Comparing Permeability and Drying Shrinkage of the Concrete Containing Mineral Admixtures under the Equal Strength Grade

Fly ash (FA) and ground granulated blast-furnace slag (GGBS) are the most widely used mineral admixtures in engineering. However, their roles in concrete under the equal strength grade, a common comparison method in engineering, were seldom reported. This study investigated the chloride ion permeability and drying shrinkage of concrete samples containing FA or GGBS under an equal strength grade. The samples’ strengths and slumps maintained the same levels by adjusting the water-to-binder ratios and superplasticizer dosages. The results show that both FA and GGBS can promote the resistance to chloride ion penetration and decrease the chloride diffusion coefficients, especially at late ages, due to the hydraulicity of GGBS and pozzolanic activity of FA. Compared with FA, GGBS presents a greater reduction in the concrete permeability due to its higher reactivity. Forty percent replacement levels of FA and GGBS can decrease the penetration level from “high” of plain cement concrete to “moderate” and “low”, respectively. In addition, FA and GGBS can decrease the drying shrinkage of concrete at high replacement levels (30% and 40%). This decrease is more significant in the FA-containing concrete, with the shrinkage decreasing from approximately 400 με to 350 με at a 40% replacement level. The findings can provide scientific guidance for applying FA and GGBS in practical engineering.

Feasibility of recycled aggregates modified with a compound method involving sodium silicate and silane as permeable concrete aggregates

Recycled aggregates (RA) used to prepare pervious concrete solve the problems of poor water permeability and lack of stone in urban pavement and achieve green and sustainable development. However, application of the recycled aggregate is difficult due to its poor performance. Treatment of the RA with sodium silicate and composite silane improves the uniformity of recycled concrete aggregates (RCAs) and recycled brick aggregates (RBAs) and reduces their porosities and pore sizes, thus improving the performance of the recycled aggregates. By using modified RA to prepare pervious concrete, the interfacial transition zones (ITZs) between RBA or RCA and the cement matrix can be improved, the widths of internal cracks and pores can be reduced, and the mechanical properties, durabilities and fatigue properties of permeable concrete (PC) can be improved. Due to the irregular shapes and relatively different RA particles, the connectivity of pores inside the PC is reduced, thus reducing the permeability of the PC. The incorporation of 30 %−70 % RA may lead to decreases in PC permeability of approximately 10 %−25 %. On the other hand, modification with sodium silicate and silane does not enhance the permeability of the PC but closes the pores inside the RA, which has an adverse effect on the permeability of the PC.

Experimental study of compressive strength, permeability and impact testing in geopolymer concrete based on Blast furnace slag

Cement production has always been associated with environmental challenges due to carbon dioxide emissions. On the other hand, cement production is an energy-intensive process and leads to the consumption of abundant fossil fuels. In order to solve this problem, the production of geopolymer concrete is on the agenda. The researchers decided to reduce the negative effects of cement production and have superior properties than ordinary concrete. In the current study, slag-based geopolymer concrete was used with 0-2% polyolefin fibers and 0-8% nano-silica to improve its structure. After curing the specimens under dry conditions at a temperature of 60°C in an oven, they were subjected to compress strength, tensile strength and Drop weight hammer tests to evaluate their mechanical properties, as well as Permeability test to assess their durability. tests were performed at 7 and 90 days of age at ambient temperature (20℃). The addition of nano-silica enhanced the whole properties of the slag-based geopolymer concrete. Increasing the curing age improved the results of all tests. The results of all tests in geopolymer concrete showed the superiority of the results over conventional concrete. At the 28-day curing age, the addition of up to 8% nanosilica to the geopolymer concrete composition improved the compressive strength test results by 19.01%, water permeability by up to 35% and impact strength by up to 36.36%. Addition of up to 2% of polyolefin fibers in the composition of geopolymer concrete resulted in a 28.95% decrease in compressive strength but a 20% improvement in water permeability and an 8.26-fold increase in impact strength. In the following, by conducting the SEM test, a microstructure investigation was carried out on the concrete samples. In addition to their overlapping with each other, the results indicate the geopolymer concrete superiority over the regular concrete. Besides, it demonstrated the positive influence of nano-silica addition on the concert microstructure.

Characteristics of GGBFS-Based Pervious Concrete Considering Rheological Properties of the Binder

To mitigate environmental challenges, such as urban flooding, noise pollution, and the urban heat island effect, pervious concrete has been developed. This research was intended to develop pervious concrete made from ground granulated blast furnace slag (GGBFS) to further decrease the environmental impact of the construction sector by reducing the content of ordinary Portland cement (OPC). The primary objective of the mix proportion was to maximize water permeability while meeting the required compressive strength. Two levels (60 and 100%) of OPC replacement by GGBFS were evaluated and compared to OPC-only concrete, and two target porosities (10 and 15%) were achieved by modifying the binder-to-aggregate ratio. CaO and CaCl2 were utilized as an activator and an accelerator, respectively, for the GGBFS only binder. Characteristics of the pervious concrete were determined with the compressive strength, porosity and water permeability test. Meanwhile, the effects of the rheological properties of binders on the water permeability and compressive strength of pervious concretes was evaluated. According to the results, the permeability of pervious concretes always exhibited a positive correlation with porosity, regardless of binder type. Although, the pervious concrete made with CaO-activated GGBFS has a lower compressive strength than the other two cases (60% GGBFS and only OPC), it still meets the minimum strength requirement. Based on the rheology studies of binder, it was found that, the adhesion force of the binder and the compressive strength of the pervious concrete decreases, as evaluated by rheology studies on binders. The CT scan revealed that when the adhesive force of the binder was weaker, the local porosity was higher (i.e., pore volume was larger) at the bottom of the specimen, which might be due to the limited consolidation and compaction of the binder between aggregate particles at the bottom due to its higher plastic viscosity.

Strength and Permeability Properties of Pervious Concrete Containing Coal Bottom Ash Aggregates.

This study investigates the strength and permeability properties of pervious concrete-containing coal bottom ash (CBA) aggregates. Two pervious concrete mixtures were fabricated with different aggregate size distributions. One mixture contained CBA aggregates with a single-type distribution and the other mixture contained CBA aggregates with a hybrid-type distribution. The test parameters of the CBA pervious concrete included the water/cement (W/C) ratio and compaction level to investigate their effects on the properties. W/C ratios of 0.25, 0.30, and 0.35 were considered for the mixture, and compaction levels of 0.5, 1.5, and 3.0 MPa were applied to fabricate the pervious specimen. The increase in the W/C ratio reduced the strength by approximately 20% to 30% of the CBA pervious concrete. The increase in the compaction level reduced the permeability by approximately four to five times but significantly increased the strength of the CBA pervious concrete. The test results indicate that the use of single-type CBA or hybrid CBA aggregates with different size distributions affected the properties of the pervious concrete. The strength of specimens, including hybrid CBA aggregates, was 30% to 45% greater than that of the specimens containing single-type CBA aggregates. Meanwhile, the use of hybrid CBA aggregates reduced the permeability of the CBA pervious concrete by approximately 20% to 35%. Finally, relationships between the strength properties, permeability characteristics and total void ratios of the CBA pervious concrete specimens are suggested based on the test results.

Application of Artificial Neural Network to Predict the Properties of Permeable Concrete

The structure of permeable concrete has been the primary reason for its use in construction. Permeable concrete is composed of water, cement, aggregate, and little- to no-fines resulting in the presence of a significant number of voids. This makes permeable concrete an ideal solution to water accumulation issues as it acts as a drainage system. This study employs a feedforward backpropagation artificial neural network model that combines experimental laboratory data from previous studies with appropriate network architectures and training techniques. The purpose of the analysis is to develop a reliable functional relationship, based on water-cement ratio, aggregate-cement ratio, and density parameters, with which to estimate the compressive strength, porosity, and water permeability of permeable concrete. Multiple linear regression correlations are also established to predict and correlate these inputs and outputs. The two derived methods are then compared and discussed. The results reveal that ANN is better to anticipate the permeable concrete properties than regression analysis.

Research on improving polymer pervious concrete mechanical strength by adding EVA to UP resin binder material

Pervious concrete (PC) made of silicate cement has advantages including low cost, low contraction, and high permeability. However, its strength and durability are lower than those of conventional cement concrete. In recent years, the resin composite material is added to the binder material to effectively improve the mechanical properties and durability of permeable concrete. Commonly used resin composites include epoxy and unsaturated polyester (UP). These resin composites are thermosetting, which cure rapidly and feature high strength and durability. The high cost and viscosity of epoxy resin limits its applications. UP is preferable to epoxy due to its lower concentration and price. This study explored the mechanical performance of high-performance PC with UP resin as the binder. Concretes were fabricated with binders of 10%, 30%, and 40% UP resin content, and specimens were mixed with 5–10-mm gravel aggregate. Compression, flexural, and abrasion testing were conducted to determine the specimen durability. The results revealed that the PC with 30% UP resin had optimal performance. UP resin is composed of a straight chain, and although it has excellent rigidity, its ductility is poor. To address this problem, thermoplastic material ethylene–vinyl acetate (EVA) was incorporated into the binder at 10%, 15%, and 20% to improve the ductility. Compression, bending, and abrasion tests showed that the addition of EVA improved the ductility and durability of the samples. Comprehensive experimental results: UP resin was matched with thermoplastic materials; EVA could improve the mechanical properties of small walking bricks with UP resin as the binder material. Durability further promotes the feasibility of a new pavement construction method from the production of a single brick.

Mechanical properties, permeability and microstructure of concrete using construction and industrial waste

PurposeThe purpose of this research is to evaluate construction and industrial waste materials in concrete using different additives.Design/methodology/approachThe experimental study investigated the effect of waste foundry sand (WFS), waste glass (GW) as partial substituent to natural sand and addition of waste glass fibers (GFs) and silica fume (SF) in natural/construction waste aggregate concrete on mechanical properties, durability and microstructure using.FindingsThe results reveal significant strength enhancement on using two admixtures, the maximum increase in compressive strength was obtained on using 20% WFS and 0.75% GF for both natural (75% increment) and construction waste (72% increment) coarse aggregates. Using three admixtures simultaneously, the maximum enhancement in compressive strength was found for (WFS(20%) + GW(10%) + GF(0.75%)) for both natural aggregates (122% increment) and construction waste (114% increment) coarse aggregates as compared to control mix. The 28 days split tensile and flexural strength of natural/construction waste aggregate concrete improve with age appreciably for optimal contents of single, two or three admixtures and the maximum tensile and flexural strength increment was 135 and 97% for mix (WFS(20%) + GW(10%) + GF(0.75%)) with natural aggregates as compared to control mix. The microstructural analysis results indicate improved microstructure upon partial substitution of sand with WFS, GW and SF along with addition of waste GFs.Originality/valueThe use of construction and industrial waste as a substituent to natural aggregate/sand will provide far reaching benefits for the green construction and the environment at large.

Mechanical properties, flexural behavior, and chloride permeability of high-performance steel fiber-reinforced concrete (SFRC) modified with rice husk ash and micro-silica

To improve the fiber-matrix bond and enhance the macro-mechanical performance of SFRC, this study is focused on the modification of the cement matrix by using two eco-friendly supplementary cementitious materials (SCMs), rice husk ash (RHA) and micro-silica (MS). The modification effects of SCMs on the steel fibers were observed and characterized by conducting several macro-mechanical tests i.e., compressive strength, splitting tensile strength, and load-deflection behavior. Besides that, ultrasonic pulse velocity, water absorption, and chloride migration tests were performed to characterize the durability of modified SFRC mixes. The results showed that the incorporation of RHA and MS at low levels notably enhanced the efficiency of steel fibers under splitting tensile and flexural strength testing. SFRC made with 7.5% MS and 7.5% RHA showed 79% and 96% more flexural strength than plain concrete (PC), respectively. Whereas SFRC experienced 14% and 26% further improvement in flexural toughness with the addition of 7.5% RHA and 7.5% MS, respectively. The addition of 7.5% and 12.5% RHA showed a beneficial effect on the resistance of SFRC against the penetration of chloride ions and water. The results of this study confirmed the synergistic interaction of steel fiber and SCMs.

Mechanisms in Long-Term Marine Corrosion of Steel Reinforcement in Concretes

This paper is concerned with the mechanisms governing reinforcement corrosion in concretes in marine environments and how they influence the manner of local failure of the concrete. Despite the high pH of the concrete, air voids from inadequate concrete compaction can, under chloride conditions, produce localized pitting corrosion of adjacent steel bars. This may continue, under the hydrogen evolution cathodic reaction with the build-up of rusts causing localized concrete failure, followed by exposure of the steel to the environment, removal of the elevated concrete pH, and a subsequent much higher rate of corrosion. A completely separate deterioration process is the gradual dissolution and loss of concrete alkalis with time. This can lower the concrete pH sufficiently to permit general corrosion of steel to be thermodynamically feasible, it increases concrete permeability and it facilitates access to the environment to permit corrosion by oxygen reduction. The two processes produce different types of concrete failure. Examples drawn from actual reinforced concrete structures are given and the mechanisms explained, including the often-observed build-up of FeOOH-type rusts on the outside of magnetite rust layers well inside concretes. The implications that follow and research needs are discussed.

Influence of stress-level due to self-weight on the hydraulic conductivity of permeable concrete for geotechnical applications

Permeable concrete is effectively used in many fields of civil and environmental engineering, including some geotechnical applications such as drainage piles, deep drainage trenches, and as a permeable backfill material for retaining walls. The principal requirements that a pervious concrete must have for geotechnical applications are those that simultaneously guarantee enough hydraulic conductivity and good filter properties against internal erosion of the soil in which the drains are realised. These requirements can be effectively achieved through special mix-designs in which a non-negligible amount of sand is added to the aggregates, unlike the permeable concretes used for example in the road construction sector where the aggregates are essentially made only of gravel and the concrete is a “no-fines” concrete. The permeability of the pervious concrete depends on many factors among which the stress level due to the self weight of the column of fresh concrete when the depth of the same column is non negligible, as it is in the geotechnical applications. Results of an experimental study on this aspect are reported in the paper. These results show that the hydraulic conductivity reduced with the vertical stress level due to the self weight of the fresh permeable concrete. This reduction is very significant in the range of vertical stress σv of 1–100 kPa (that correspond to the self-weight of a column of “classical” fresh pervious concrete h* ranging from about 0.1 to 6 m). Subsequently this reduction is less marked up to the maximum stress level reached in the tests (σv=700kPa, h* about 40 m). The minimum hydraulic conductivity (hydraulic conductivity for σv=700kPa) is, however, still sufficient and adequate for draining medium to fine-grained base soils (soil near piles or trench drains) such as clays, silty-clays, sandy-silts, silty-sands, and fine sands.

Martian and lunar sulfur concrete mechanical and chemical properties considering regolith ingredients and sublimation

• Sulfur sublimation rate at vacuum is 8000 times lower at −60 °C than at 20 °C. • Sulfur concrete permeability decreases strongly with higher sulfur content. • Sulfur concrete porosity does not change much with varying sulfur content. • The presence of alumina in sulphur concrete results in higher porosity. • Alumina and iron oxide together in sulphur concrete leads to lower porosity. Space constructions require unique materials suitable for the harsh conditions in space. Sulfur concrete (SC) is one of the most promising materials for such applications. However, the behavior of sulfur concrete in a vacuum, microgravity, and different temperature conditions and its chemical changes has not been well established yet. This study investigated the effect of vacuum, sulfur content, and compaction (trowel effect) on mechanical and hydro-mechanical properties. Moreover, this study assesses the impact of chemical reactions of aluminum and iron oxides with molten sulfur on the sulfur concrete’s mechanical properties via X-ray diffraction analysis (XRD), scanning electron microscopy (SEM-EDS), and Fourier-transform infrared spectroscopy (FTIR). The predictions from this research show that the sublimation rate under vacuum conditions at very low temperature (−60 °C) can be reduced nearly 8000 times compared with that at 20 °C according to the vapor pressure-sublimation rate relationship. In addition, mechanical experimental tests show that a slight increase in sulfur content dramatically reduces the permeability of sulfur concrete. On the other hand, the porosity is not much affected by the sulfur content. Moreover, sample compaction leads to a significant reduction and increment of the hydro-mechanical and mechanical strength, respectively, indicating the trowel's positive effect. Chemically, sulfur dioxide reacts with alumina and iron oxide via chemical adsorption, and then reaction with molecular oxygen produces S O 4 2 - confirmed by SEM-EDS, XRD, and FTIR results. The presence of alumina increases the sample porosity, although, together with iron oxide, another mineral, namely A l 2 F e 2 S O 4 6 ( H 2 O ) 12 . 6 H 2 O (Aluminocoquimbite), is formed resulting in a lower porosity. To conclude, we have shed light on sulfur concrete properties and preparation processes in unconventional environments and we have shown how different unknown parameters affect the mechanical and chemical properties of the sulfur binder.

A Comparative Study on Water and Gas Permeability of Pervious Concrete

The water and gas permeability of pervious concrete play essential roles in rainwater infiltration and plant root respiration. In this study, the gas and water permeability of pervious concrete samples were measured and compared. The water permeability was tested using the constant water head method and several water heads were measured for inspection, in which the permeability varied with the application of the pressure gradient. The permeability of gas was measured using a new simple gas permeameter, which was specially manufactured for measuring the gas permeability of pervious concrete under a stable pressure difference. A series of different gas pressure gradients was applied to test whether the gas permeability was a function of the applied pressure. Both the gas and water permeability of pervious concrete were found to decrease with an increased applied pressure gradient, which did not conform to the Klinkenberg effect (gas slippage effect). When comparing the gas permeability and water permeability of pervious concrete, we found that the water permeability was 4–5 times larger than the gas permeability.

Use of Concrete Waste from Industries as an Alternative Material for the Permeable Concrete Production

Every year, tons of demolished concrete waste items dump into the environment from the construction industry. With this process, a massive environmental pollution occurs. Therefore, in this research, the main aim is to find a solution for this environmental pollution by recycling this waste products. The main objective is to recycle these concrete waste materials from industries to use as an alternative material for the production of permeable concrete by maintaining the recommended compressive strength and the recommended permeability. Permeable concrete can be used for the concreting of floor areas like car parks. It provides environmentally friendly way to drain storm water without flooding. For this research, cement to aggregate ratio was used 1:5 and 14mm to 20mm size natural coarse aggregate and concrete waste were used. The control sample was prepared using 100% aggregate. With total amount of aggregate weight 5%, 10%, 20%, 30%, 40% amounts were replaced with the waste concrete after preparing 14mm to 20mm size samples. The slump test, compressive strength test and the permeability tests were conducted. According the results of the 28 days compressive strength test, the control sample was obtained 7.423MPa strength but neither of any other sample could not reached this strength. However, the sample which replaced with the 10% of waste concrete with 90% natural coarse aggregate has obtained 88.683% strength compared to the control sample. According to the permeability results it shows that there will not have a great impact by using concrete waste as an alternative material in permeable concrete production. The results were varied between 15.8L/m2/s to 15.08L/m2/s.

Investigation on Carbonation and Permeability of Concrete with Rice Hush Ash and Shop Solution Addition.

The goal of this study was to determine the coefficient of permeability as well as the rate of carbonation of concrete constructed with rice husk ash (RHA) as a partial replacement for cement (i.e., 5%, 10%, and 15%) and two different concentrations of soap solutions (i.e., 1 percent and 2 percent). The microstructural studies of RHA, and carbonated samples have been conducted by using Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) analysis. According to this study, the carbonation depth of concrete made with 1% and 2% soap solution concentration and without rice husk ash decreased by 11.89% and 46.55%, respectively. From the results, it may also be observed that the carbonation depth of concrete made with up to 10% replacement of cement by rice husk ash led to maximum carbonation resistance, while more than 10% replacement of cement showed higher carbonation depth. It is also observed that the coefficient of permeability of concrete with 2% soap solution significantly decreased as compared to the 1% soap solution and control mix. It may be observed from the SEM images that 0% soap solution (M1) concrete has a very rough concrete surface which may indicate more voids. However, 2% soap solution concrete has a much smoother surface, which indicates a smaller number of voids. Furthermore, the SEM images showed that the soap solution helps in filling the voids of concrete which ultimately helps in reduction in permeability. Energy Dispersive X-Ray Analysis (EDX) of concrete with 0% (M1) and 2% (M6) soap solution disclosed that the concrete with 2% soap solution (M6) exhibited more silica element formation than the concrete with no soap solution (M1).

Workability, Strength, Modulus of Elasticity, and Permeability Feature of Wheat Straw Ash-Incorporated Hydraulic Cement Concrete

The extensive use of Portland cement (PC) in the manufacturing of concrete is responsible for the depletion of natural resources that are part of cement production. Cement supply is permanently threatened by the ongoing depletion of natural materials, including sand, limestone, and clay. Concurrently, the incineration of agricultural residues presents a significant ecological problem. This study explores the substitution of cement in concrete with 5%, 10%, 15%, and 20% wheat straw ash as an environmentally friendly alternative. The purpose of this investigation is to evaluate the effect of substituting wheat straw ash (WSA) for PC on the mechanical characteristics of concrete. A total of 75 concrete samples were made by cement or cement + WSA/fine aggregate/coarse aggregate ratio of 1:1, 5:3, and water-to-cement ratio was kept constant at 0.50. All of these specimens were cured and tested at 28 days. The properties tested in the paper were workability, compressive strength, splitting tensile strength, flexural strength, modulus of elasticity, and permeability. The outcomes showed that the substitution of PC with WSA 10% resulted in the greatest concrete strength. In contrast, the mechanical properties and permeability of concrete were reduced when 20% WSA was substituted for PC at 28 days. In addition, the slump value dropped as increasing the content of WSA diminished the weight of PC in the concrete. This could be attributed to the fact that the water content in the WSA 20% concrete was not enough for mechanical strength. Other concretes with WSA showed similar properties to those of the WSA 10% concrete. It was concluded from the results that since the WSA 10% concrete showed the best properties, it can be recommended as the best recipe in this research work.

Correlating damage and cracking with air (gas) permeability in concrete using the Brazilian tension test

• Using acoustic emission and digital image correlation in the indirect Brazilian tension test, damage and cracking can be correlated to gas permeability in concrete. • A microcrack size of 40 µm can distinguish between pre-cracking and post-peak behavior of concrete. • Gas permeability of concrete increases to almost half an order of magnitude in the pre-peak region. • Gas permeability of concrete increases to about six orders of magnitude during the progression of cracking in the post-peak region. This article investigates the relationship between stress, damage, crack propagation, and air (gas) permeability evolution in concrete using the Brazilian tension test. This investigation is important for situations where hazardous gases are in contact with concrete as it quantifies the effect that damage of concrete has on gas permeability. Cylindrical concrete disc specimen of diameter 101.6 mm and thickness 50.8 mm were used for this study. Acoustic emission sensors are used to observe damage occurrence and propagation in the concrete, while a digital image correlation set-up is used to precisely measure the crack opening displacement. A vacuum flow system is attached to the rear side of the concrete under loading to measure apparent air permeability through the concrete specimen before and after cracking. The collected data is synchronized and analyzed to correlate damage and crack propagation and air permeability evolution in concrete under tension stresses. It was found that the air (gas) permeability increased by over six orders of magnitude as the concrete cracking occurs and changes in air (gas) permeability directly correlate with changes in concrete damage and fracture.