Compressive Strength Loss Research Articles

Rice husk ash and recycled sand as synergistic substitutes in ultra-high performance concrete: Microstructural, mechanical performance, and eco-economic analysis

Quartz sand and silica fume (SF), commonly used in UHPC production, are costly and contribute to dust pollution and significant carbon emissions. In this work, we explored the preparation of an environmentally friendly ultra-high performance concrete (e-UHPC) by substituting SF and quartz sand with rice husk ash (RHA) in ratios of 10 %, 20 %, and 30 %, and recycled building sand (RS) in ratios of 25 %, 50 %, and 75 %. We assessed the impact of these substitutions on workability, mechanical strength, hydration products, and the micromechanical characteristics of the interfacial transition zone. In addition, an environmental and economic assessment index for e-UHPC was introduced. Results showed that while RHA and RS reduced the flowability of e-UHPC, RHA helped mitigate the compressive strength loss due to RS (3.9 %-9.7 %). RHA accelerated early hydration, and improved densification in the transition zone, enhancing late hydration and refining the pore structure of e-UHPC. Notably, a 10 % RHA replacement rate optimally improved early hydration efficiency and minimized CH content. The combination of 10 % RHA and 25 % RS proved most effective in optimizing the interfacial transition zone and improving the pore structure of e-UHPC. Importantly, e-UHPC reduces the carbon footprint at a lower cost and offers significant environmental and economic advantages over traditional UHPC. The results of this study will promote the incorporation of construction and agricultural wastes into concrete.

Enhancing thermo-mechanical and moisture properties of 3D-Printed concrete through recycled ultra-fine waste glass powder

This paper presents a novel approach to enhancing 3D printed concrete (3DPC) by incorporating ultra-fine glass powder (UFGP), focusing on its mechanical properties and high-temperature resistance. Investigation like fresh properties, basic physical properties, residual compressive strength after exposure to 400 °C and 800 °C, hygric properties such as water vapor diffusion resistance, liquid water transport, and moisture buffering capacity were performed the observe the effect of UFGP replacement ratio on 3DPC, which demonstrates significant improvements, highlighting the potential of UFGP to elevate 3DPCs’ performance. Results showed significant improvements, particularly with a 20% UFGP mix, which showed the lowest compressive strength loss (9.0% at 400 °C and 53.7% at 800 °C). Additionally, the water vapor diffusion resistance factor for the 20% UFGP mix was measured at 65.03. These results suggest that incorporating UFGP in 3DPC enhances thermal resilience and mechanical properties, offering a solution for high-temperature construction. This study contributes to sustainable construction by emphasizing the importance of mechanical resilience for structural integrity under extreme temperatures.

Effect of Olive Waste Ash as a Partial Replacement of Cement on the Volume Stability of Cement Paste

Over the last decades, concrete has been excessively prone to cracks resulting from shrinkage. These dimensional changes can be affected by the incorporation of supplementary cementitious materials. This work used olive waste ash (OWA), which could substantially tackle this problem and achieve sustainability goals. For this issue, five cement paste mixes were prepared by replacing cement with OWA at different percentages varying from 0 to 20% by weight with a constant increment of 5%. The water-to-cement ratio was 0.45 for all mixes. Compressive strength and flexural strength were investigated at 7, 28, and 90 days. In addition, three shrinkage tests (drying, autogenous, and chemical) and expansion tests were also conducted for each mix and measured during 90 days of curing. The experimental findings indicated that there was a loss in compressive and flexural strength in the existence of OWA. Among all mixes containing OWA, the samples incorporating 10% OWA exhibited maximum strength values. Furthermore, the chemical and autogenous shrinkage decreased with the incorporation of OWA. However, the drying shrinkage decreased at lower levels of substitutions and increased at higher replacement levels. In addition, there was a growth in expansion rates for up to 10% of OWA content, followed by a decrease at higher levels (beyond 10%). Additionally, correlations between these volumetric stability tests were performed. It was shown that a positive linear correlation existed between chemical shrinkage and autogenous and drying shrinkage; however, there was a negative relationship between chemical shrinkage and expansion.

Study on the Effect of Basalt Fiber Content and Length on Mechanical Properties and Durability of Coal Gangue Concrete

The massive accumulation of coal gangue not only causes a waste of resources but also brings serious environmental pollution problems. To promote the utilization of coal gangue resources, mitigate environmental pollution from coal gangue, and address the shortage of natural aggregates, this study investigates the use of coal gangue to replace coarse aggregate at a 40% replacement rate to prepare coal gangue concrete (CGC). The current research on the modification of gangue concrete by BF has been less often compared with the research on the effect of basalt fiber (BF) on the properties of ordinary concrete, so in this study, BF with different admixtures and lengths were added into CGC. Additionally, basalt fibers (BFs) of varying amounts and lengths were incorporated into CGC. The study explored the effects of BF on the tensile strength, splitting tensile strength, and flexural strength of CGC. It was found that the mechanical properties of CGC improved significantly when the BF dosage was 0.10–0.15% and the length was 18 mm. This is evidenced by an increase in the compressive strength of 3.94–5.11%, split tensile strength of 11.20–16.18%, and flexural strength of 8.23–12.97%. BF was able to refine pore space, prevent crack development, and bridge cracks in CGC. To further investigate the effect of BF on the long-term service performance of CGC, the effects of BF on the appearance, quality, and compressive strength of CGC in sulfate and freeze–thaw environments were examined. The results indicated that a BF dosage of 0.10–0.15% significantly enhanced the sulfate erosion resistance and freeze–thaw resistance of CGC. This is shown by a 36.76–46.90% reduction in the rate of loss of compressive strength of CGC under the freeze–thaw cycling and a 6.21–8.50% increase in the corrosion resistance factor of CGC under a sulfate attack. BF improved the pore structure and reduced seepage channels, thereby enhancing the durability of CGC.

Degradation mechanism and strength prediction of aeolian sand concrete under sulphate dry-wet cycles

In this paper, aeolian sand (AS) with different contents (0 %, 25 %, 50 %, 75 % and 100 %) was used as fine aggregate to prepare aeolian sand concrete (ASC). The effects of AS content and dry-wet cycle (DWC) times on the durability of ASC under sulfate (5 % Na2SO4) erosion conditions were investigated by DWC tests. The mass loss rate, compressive strength loss rate and relative dynamic elastic modulus (RDEM) were used as the macroscopic performance evaluation indexes, while the damage degradation mechanism of ASC was revealed by combining the microscopic technical means such as SEM, XRD, TG-DSC and NMR. The results show that the macroscopic properties of ASC under the action of DWC of sulphate all show the first increase and then decrease, as when the dosage of AS is below 50 %, the "bead effect" and "padding effect" of AS can further improve the internal densification of ASC, thus effectively resisting external sulphate erosion. During sulphate erosion, SO42- firstly reacts with cement hydration product Ca(OH)2 to generate erosion products such as Ettringite (AFt) and fills them within the original defects, with short-term rnhancement of macroscopic properties. As the DWC continue, the excessive erosion products accumulated, resulting in the destruction of pore structure and extension through the phenomenon, the matrix compactness is reduced, and the macroscopic properties degraded. The grey entropy correlation analysis yielded that the grey entropy correlation grade of bound fluid saturation, harmless pore percentage and less harmful pore percentage with compressive strength were all above 0.8, and the GM(1,4) strength prediction model established on the basis of the above pore structure parameters has a high prediction accuracy, and the relative errors between the predicted strength values and the actual strength values are within 10 %, and the research results can provide certain theoretical support for the study of the durability of ASC in sulfate erosion environment.

Effect of test related factors on the degradation of cement-based materials on acetic acid exposure

Abstract Exposure of concrete to various acids can hardly be overstated due to the widespread use of concrete in the construction industry. The effect of selected factors on the degradation of ordinary Portland cement (OPC 53 grade) paste and mortar exposed to acetic acid is investigated in this paper. Various test parameters such as mass loss, loss in cross-sectional area, relative dynamic elastic modulus (RDEM), loss in flexural and compressive strength are used to assess the selected factors and the results obtained are analysed to determine the most favourable test conditions for degradation, that can be adopted for developing an accelerated test method. The factors used for the investigation are replenishment of acid solution, concentration of acid solution, ratio of surface area of specimen to volume of liquid acid solution (S/L), shape of the specimen and nature of the specimen. This paper also investigates the interrelationships among test parameters and adopts interpretation of acid consumption to assess the aggressiveness of the acid solution. It was found that renewing conditions and high concentrations of acid solution (0.5 M) indicate rapid degradation. The aggressiveness of 0.125 M acetic acid solutions in renewing conditions is about 5 times that of non-renewing conditions respectively. The rate of degradation is inversely related to S/L ratio. Cylindrical specimens have a marginal increase in degradation than prismatic specimens. It is preferable to evaluate acid attack on mortar specimens rather than paste specimens due to higher loss in cross-sectional area and relative dynamic elastic modulus (RDEM).

Effect of Polypropylene Fibers on the Behavior of Dune Sand Concrete Subjected to Elevated Temperatures

In the field of civil engineering, concrete is one of the most used materials. Above a particular temperature, concrete can exhibit thermal instability during fire events. Improving the safety of buildings and structures is an important issue of this study. This paper investigates the effects of adding polypropylene fibers to dune sand concrete at high temperatures. Prismatic specimens (4 x 4 x 16 cm3) are produced, and stored until the concrete is hardened. The samples are then subjected to a heating-cooling cycle, starting from room temperature and increasing by 0.1 °C/min until reaching 600 °C. The length and the rate of polypropylene fibers are examined to determine their impact on compressive strength, porosity, and weight loss at temperatures of 80, 150, 300, 450, and 600 °C. Also, the partial replacement of dune sand (DS) with river sand (RS) is investigated. The results show that, for temperatures below 450 °C, the strengths of dune sand concretes varied from 29 to 39% compared to those obtained with concretes subjected to an ambient temperature (20 °C). However, it should be noted that residual compressive strength values decrease at most temperatures with the addition of polypropylene fibers. Furthermore, sand concrete with 50% DS and 50% RS shows an increase in compressive strength of 43.77% compared to that obtained by 100% DS concrete.

A new proposal to reduce microplastics from cigarette butts: Production of eco-friendly fired clay bricks

It is estimated that approximately 1.2 million tons of cigarette butts (CBs) are introduced into the environment annually. The aim of this work is to analyze the incorporation of shredded CBs into bricks making by extrusion, for recycling and waste recovery purposes. Samples were prepared in compositions of 0 %, 1 %, 2.5 % and 5 % w/w CBs and fired at 700 ºC, 900 ºC and 1000 ºC. Density, water absorption, apparent porosity, linear firing shrinkage, flexural strength, compressive strength, thermal conductivity, diffusivity and sound transmission loss (TL) were determined. A total of 180 samples were taken, and a Weibull statistical analysis was performed for compressive strength. The results showed a decrease in density and an increase in water absorption and apparent porosity of the clay bricks produced by mixing 1–5 % CBs compared to the control bricks. Firing shrinkage decreased with 1 % CBs and up to 2.5 %, its was lower than standard samples. Samples with CBs showed fewer cracks than standard samples. Compressive strength increased with 1 % CBs incorporation for firing temperatures of 900ºC and 1000ºC compared to standard samples. It gradually decreased with larger amounts of waste. For flexural strength, up to 2.5 % CBs, the strength increased in most cases. In addition, there was an improvement in the thermal conductivity of bricks prepared with 5 % CBs and fired at 700ºC and 900ºC (0.46–0.58 W/mK) compared to the reference samples (0.51–0.76 W/mK). All waste samples showed higher TL than the reference pieces. Above 2.5 % CBs, TL decreased, but remained larger than the reference. Thus, the results showed that the use of CBs in fired clay bricks in amounts of up to 5 % w/w is capable of forming porosity in the samples, making the part lighter, in addition to possibly reducing thermal conductivity and sound transmission, being an economical and sustainable alternative for the final disposal of CBs.

Synthesis of a chitosan-based superabsorbent polymer and its influence on cement paste

To address the challenge of adaptability between cement-based materials and conventional superabsorbent polymers (sodium polyacrylate, Na-PA), a chitosan-based superabsorbent polymer (CSP) with high salt and alkaline resistance was synthesized, and the optimal synthesis process was determined by a single-factor method. The macroscopic performance and microstructure of CSP and Na-PA were compared, and their influences on cement paste were studied. The results show that CSP exhibits a gradual swelling process during water absorption, which is independent of the solution environment. The poriferous structure of CSP allows it to form a network composed of gel membranes. The introduction of amide group enhances the resistance of CSP to salt and alkaline conditions. The autogenous shrinkage of cement paste is mitigated by CSP, with a superior effect compared to Na-PA. The longer desorption time of CSP allows it to promote cement hydration for a longer period, reducing the loss of compressive strength. The heat release, chemically bound water and hydration products (portlandite and amorphous substances) of CSP pastes are higher than those of Na-PA pastes. The water desorption from CSP fills some middle capillary pores and mesopores, leading to the pores in the hardened cement paste being more concentrated in smaller sizes.

Modification of the polymeric admixture based on polycarboxylate ether using silica-derived secondary materials obtained from fly ash and the efficiency of its application in concrete

The rising energy prices and the costs of CO2 emissions into the atmosphere are forcing the construction industry to search for ways to reduce cement consumption in concrete technology by optimizing concrete mixtures and making greater use of chemical admixtures. The scientific problem lies in understanding how polymers modified with silica-derived secondary materials, such as those obtained from fly ash (e.g., synthetic zeolites, mesoporous silica), interact with the concrete matrix and influence their durability and strength. The present study investigated the effect of a polymeric admixture based on polycarboxylic ether (PCE) modified with silica-derived secondary materials obtained from fly ash (synthetic zeolites, mesoporous silica) on the physical and mechanical properties of concrete. The study considered the effect of the modified polymer admixture dosed in 3 different amounts (0.4%, 0.8% and 1.2%) by weight of cement on the fresh properties of the concrete mixture, i.e. consistency and air content. The research scope also included determining the physico-mechanical properties of the concretes and investigating the effect of the modified admixture on the frost durability of the cement composite. In order to study the modification of the concrete microstructure, XRD phase analysis and air pore structure analysis by MIP were carried out. The study showed an increase in compressive strength after 28 days of curing in concretes containing the modified polymer of about 8-12% compared to the reference concrete. In addition, it was observed that strength increased with increasing admixture dosage. The resulting pore structure, contributed to improving the frost resistance of the concretes by reducing compressive strength loss from about 14% in reference concretes to about 2-9% in concretes with the modified polymer after 150 cycles of alternating freeze-thaw. At the same time, it was observed that the use of the modified polymer resulted in an increase in weight absorption from 2% do 4.5%, a more than twofold increase in depth of penetration of water under pressure and a more than 70% increased total porosity. In conclusion, the polymer-modified MCM-41 can positively affect the mechanical and durability properties of concrete, but it causes a change in the pore structure, which could have a negative effect on water absorption and total porosity.

Studies on the performance of alkali-activated aluminosilicate geopolymer mortar against exposure to acid, sulfate, and elevated temperature

An alkali-activated aluminosilicate is a group of materials that have the potential to reduce the carbon footprint of the construction industry. Several combinations of materials have been explored for producing alkali-activated aluminosilicate geopolymer mortars, emphasizing the need to understand their resistance to chemical attack and elevated temperatures to ensure long-term durability. The present study prepared fly ash-based alkali-activated aluminosilicate mortar using fly ash (FA) and ground granulated blast furnace slag (GGBS) without heat curing. Properties such as compressive strength and weight loss were evaluated after chemical attack and exposure to high temperatures (200° to 1000°), and compared with PC mortars. The result shows that fly ash and GGBS-based alkali-activated aluminosilicate mortar (AAAM) exhibit better resistance to chemical attack and high temperatures than conventional mortar. Specifically, after 180 days of acid exposure, PCM showed a mass loss of 5.06% and compressive strength loss of 85%, while AAAM had a mass loss of 2.88% and compressive strength loss of 71%. Sulfate exposure led to a mass gain of 55.77% for PCM and 27.35% for AAAM, with compressive strength losses of 55.77% for PCM and 27.35% for AAAM. Elevated temperatures (1000°) resulted in a compressive strength loss of 68% for PCM and 45% for AAAM. To substantiate these results, X-ray diffraction (XRD) and Fourier Transformation Infrared Spectroscopy (FTIR) were used to study the changes in the bonding behavior of C-A-S-H (Calcium-Aluminate-Silicate-Hydrate) and N-A-S-H (Sodium-Aluminate-Silicate-Hydrate) when exposed to chemical attack and elevated temperatures.

Impact of Rubber Content on Performance of Ultra-High-Performance Rubberised Concrete (UHPRuC)

This study investigated the effect of rubber content on the mechanical characteristics of ultra-high-performance rubberised concrete (UHPRuC). The results revealed a distinctive non-linear decrease in the dry density of UHPRuC as the rubber content increased. Notably, lower rubber content led to a columnar failure mode, while higher content (≥ 20%) exhibited a mixed failure mode with vertical cracking and diagonal fracture. Importantly, the compressive strength showed minimal reduction compared to conventional concrete, presenting a remarkable 50% mitigation of strength reduction compared to previous studies. Utilising reference concrete with robust bond strength proved highly effective in preserving strength in rubberized concrete. Despite its effectiveness in mitigating compressive strength reduction, UHPC could not effectively offset flexural strength loss, which ranged from 1.5 to 3 times that of compressive strength loss. The addition of rubber aggregate in UHPC reduced the peak flexural strength, residual strength, and flexural toughness at a similar rate, while significantly increasing the vibration decaying rate. Incorporating 40% rubber in UHPRuC reduced the eCO2 up to 37%. Our findings emphasise the importance of reference concrete with good bond strength and shows that the addition of rubber aggregate in UHPC leads to reductions in strength but increases the energy-dissipating capacity.

Assessing the Durability Performance of Geopolymer Concrete Utilizing Fly Ash and Sugarcane Bagasse Ash as Sustainable Binders

Geopolymer or alkali-activated binders are being recognized as an eco-friendly, sustainable substitute for ordinary Portland cement (OPC). The development of high-performance concrete with improved durability and mechanical properties and the addition of environmentally friendly components is a continuous effort. Therefore, the current work examines the durability of fly ash-sugarcane bagasse ash mechanical characteristics in terms of water absorption, exposure to elevated temperatures, and acid resistance. The mechanical properties of the geopolymer concrete (GPC) and OPC concrete specimens were evaluated after being subjected to elevated temperatures of 200 °C, 400 °C, 600 °C, and 800 °C. The acid resistance was determined by submerging the concrete specimens in 3% sulphuric acid (H2SO4). The acid resistance of the specimens was evaluated through visual inspection, weight variation, and the percentage loss in compressive strength (CR). According to the study, CR typically drops as temperature increases from ambient temperature to 800 °C. However, the rate of decline reduced as temperature increased from ambient temperature to 200 °C. Moreover, the GPC specimens showed a strength loss between 13% and 21% following 28 days of sulfuric acid immersion. In contrast, exposure to sulfuric acid caused a 51% drop in strength for the OPC concrete samples.

Study on the Effect of Silica–Manganese Slag Mixing on the Deterioration Resistance of Concrete under the Action of Salt Freezing

The use of silico-manganese slag as a substitute for cement in the preparation of concrete will not only reduce pollution in the atmosphere and on land due to solid waste but also reduce the cost of concrete. To explore this possibility, silico-manganese slag concrete was prepared by using silico-manganese slag as an auxiliary cementitious material instead of ordinary silicate cement. The mechanical properties of the silico-manganese slag concrete were investigated by means of slump and cubic compressive strength tests. The rates of mass loss and strength loss of silico-manganese slag concrete were tested after 25, 50, and 75 cycles. The effect of the silica–manganese slag admixture on the microfine structure and properties of concrete was also investigated using scanning electron microscopy (SEM). Finally, the damage to the silica–manganese slag concrete after numerous salt freezing cycles was predicted using the Weibull model. The maximum enhancement of slump and compressive strength by silica–manganese slag was 17.64% and 11.85%, respectively. The minimum loss of compressive strength after 75 cycles was 9.954%, which was 34.96% lower than that of the basic group. An analysis of the data showed that the optimal substitution rate of silica–manganese slag is 10%. It was observed by means of electron microscope scanning that the matrix structure was denser and had less connected pores and that the most complete hydration reaction occurred with a 10% replacement of silica–manganese slag, where an increase in the number of bladed tobermorite and flocculated C-S-H gels was observed to form a three-dimensional reticulated skeleton structure. We decided to use strength damage as a variable, and the two-parameter Weibull theory was chosen to model the damage. The final comparison of the fitted data with the measured data revealed that the model has a good fitting effect, with a fitting parameter above 0.916. This model can be applied in real-world projects and provides a favorable basis for the study of damage to silica–manganese slag concrete under the action of salt freezing.

Study of Ultra-High Performance Concrete Mechanical Behavior under High Temperatures.

The main concern with concrete at high temperatures is loss of strength and explosive spalling, which are more pronounced in high-strength concretes, such as Ultra-High Performance Concrete (UHPC). The use of polymeric fibers in the mixture helps control chipping, increasing porosity and reducing internal water vapor pressure, but their addition can impact its mechanical properties and workability. This study evaluated the physical and mechanical properties of UHPC with metallic and PVA fibers under high temperatures using a 23 central composite factorial design. The consistency of fresh UHPC and the compressive strength and elasticity modulus of hardened UHPC were measured. Above 300 °C, both compressive strength and elasticity modulus decreased drastically. Although the addition of PVA fibers reduced fluidity, it decreased the loss of compressive strength after exposure to high temperatures. The response surface indicates that the ideal mixture-1.65% steel fiber and 0.50% PVA fiber-achieved the highest compressive strength, both at room temperature and at high temperatures. However, PVA fibers did not protect UHPC against explosive spalling at the levels used in this research.

Mechanical strength and durability of GBFS geopolymer modified with metakaolin and functionalized beta-silicon carbide whiskers

Durability is crucial for materials development in construction and transportation industries. This paper investigates the mechanical strength and durability of alkali-activated granulated blast-furnace slag (GBFS) and modified geopolymer with varying contents of metakaolin (MK) and functionalized beta-silicon carbide whiskers (β-SiCw). Functionalized β-SiCw were prepared utilizing successful chemical methods. Macroscopic experiments tested mechanical strength, bulk density loss rate after exposure to severe conditions, and durability through sulfate wet-dry and freeze-thaw cycles. Microscopic experiments, including SEM-EDS, XRD, TG-DSC, and BET, revealed the microstructure mechanisms. Results showed that MK and functionalized β-SiCw improved mechanical strength by creating a more reactive phase and denser pore structures. Reduced bulk density loss rates and enhanced durability were observed, with a 71.9 % mass loss and 63.4 % compressive strength loss reduction after 50 freeze-thaw cycles, and a 12.2 % decrease in compressive strength loss after 56 days of sulfate wet-dry cycles, compared to control groups. The modified geopolymer had higher tortuosity and finer porosity due to more gel formation and nucleation sites, and functionalized β-SiCw effectively bridged micro-cracks and micro-pores.

Attaining material circularity in recycled construction waste to produce sustainable concrete blocks for residential building applications

Construction waste poses a major environmental problem owing to traditional building methods, resulting in a huge global waste burden that ultimately ends up in landfills. The development of sustainable methods is necessary not only to reduce environmental problems but also to encourage material circularity and promote the effective recycling and reuse of construction waste. Yet, previous research has largely focused on using recycled construction waste as a single or double additive ingredient. However, this study aims to assess the development of sustainable concrete blocks for residential building applications with a novel blend of two or more waste ingredients, with each additive contributing to a specific characteristic. Physical properties (bulk density, porosity, water absorption, thermal conductivity, compressive strength, fire resistance, and mass loss), cost, and CO2 emissions were determined to evaluate the efficiency of the block. Subsequently, the energy savings were assessed using block samples as single-layer building envelopes within a full-scale room simulated using EnergyPlus. The results showed a reduction in density of up to 24.32 %, and thermal conductivity and heat transfer of up to 56.8 % compared to typical blocks, which satisfied the compressive strength requirements of load- and non-load-bearing walls. The sustainability assessment revealed that the developed concrete blocks could significantly lower production costs by up to 31.75 % and reduce carbon emissions by up to 27.15 % compared to typical concrete blocks. It was found that the best single-layer building envelope in a full-scale residential room improved energy efficiency by up to 9.17 % when the produced blocks were used. This enhancement could lower the cost of energy consumption from 88.34 to 80.24 kWh/m2/year. This research contributes to the utilization of circular building blocks, which reduce the need for typical raw materials while improving their functional properties and lowering the production cost, carbon emissions, and energy consumption in a single-layer residential building.

Exploring innovative resilient and sustainable bio-materials for structural applications: Hemp-fibre concrete

Traditional construction is no longer practical in the modern competitive sustainability market, and growing urbanisation demands are paralleled by heightening concerns over the depletion of natural resources. Abundant renewability is offered in agriculture products for construction. A successful prototype is in the use of natural fibre, e.g., the commercially available hemp fibre (HF). Hemp is a widely accessible plant with flexible and sustainable cultivation processes possessing a positive carbon sequestration effect. HF possesses superior physio-mechanical properties, such as high tensile strength and excellent insulation capacity. The barrier to broader adoption lies in the nonuniformity inherent to natural materials and deficiencies imposed in using HF for composites, such as heightened permeability and slow setting, presenting engineering challenges that limit the suitability of HF to hydraulic mortars for non-structural applications. This paper aims to deliver a comprehensive state-of-the-art review of existing hemp fibre-reinforced concrete (HFRC) experiments towards identifying structural potential in various cementitious binders. In experimenting different arrangements of hemp in concrete, positive outcomes include increased flexural capacity, however, a loss in compressive strength and higher permeability are reported.

Electrical characterization of freeze-thaw damage in saturated concrete and its interfacial transition zones

Determining the freeze-thaw (F-T) damage of the interfacial transition zone (ITZ) is crucial to understanding the mechanism of F-T in concrete and improving its frost resistance. In this paper, the F-T damage of saturated concrete/mortar and ITZ is characterized using AC impedance spectroscopy, and the micro-mechanisms of F-T damage in cement-based materials (CBMs) are summarized. Firstly, the damage factor was defined by the effective resistivity of the CBMs, and a correlation between the damage factor and the compressive strength loss was established. The F-T damage process was divided into a damage development stage and a damage stabilization stage based on the damage factor and fractal dimension. Then, the effective resistivity separation formula was proposed to calculate the ITZ effective resistivity, and the ITZ damage factor was calculated for non-destructive quantitative characterization of the F-T damage in the ITZ. Finally, the microscopic mechanism of F-T damage in CBMs and their ITZs was summarized based on damage factor, fractal dimension, super depth of field microscopy, and nanoindentation. The results showed a linear relationship between the damage factor and compressive strength loss (Lc = 0.176Er+0.030); the ITZ had damage factors of 80 % and 70 %, which were 1.6 and 1.4 times higher than those of the matrix, respectively; F-T cycles produce micro-damage, part of which connects with the disconnected pores to form connected pores, the micro-damage extends and accumulates along the surface of the aggregates, leading to ITZ debonding from aggregate and deterioration of the mechanical properties.

Mechanical properties, hydration behavior and shrinkage deformation of ultra-high performance concrete (UHPC) incorporating MgO expansive agent

To reduce the extremely high autogenous shrinkage deformation of ultra-high performance concrete (UHPC) caused by low water-to-binder ratio and high binder materials content, this work aimed to designed and prepared low shrinkage UHPC containing MgO-based expansive agents (MEA). The effects of UHPC with different reactivity of MEA (R-MEA and S-MEA) were compared in terms of fluidity, mechanical properties, hydration characteristics, shrinkage deformation, pore structure and microstructure. The results indicated that the incorporated of MEA decreased the fluidity and mechanical properties of UHPC, while the autogenous shrinkage deformation was compensated significantly. When 6 % R-MEA was incorporated, the flow and compressive strength decreased by 16 % and 7.9 %, respectively, but the autogenous shrinkage at 7 days also decreased by 70.1 % at the same time. The same amount of S-MEA showed lower compensation for the autogenous shrinkage of UHPC than R-MEA, but with the same reduction in compressive strength loss. This was due to the highly reactive R-MEA showed higher hydration degree and larger swell increment, which caused more compensation for shrinkage in UHPC, while it had slight adverse effect on the strength development. It is worth noting that the compensation effect of autogenous shrinkage is very limited when the doping is higher than 6 % for either MEA, but the loss of mechanical properties is serious. In addition, the microstructure showed that the crystal growth pressure of brucite forced the pastes to expand and thus resulted in increase on the porosity for UHPC. This study provides a feasible and effective way for mitigating the autogenous shrinkage of UHPC.