Search Results (20)

This study examines the effect of air-entraining agents (AEAs) type on cement-mortar air content and air-void structure under reduced atmospheric pressure. Six representative AEAs—cetyltrimethylammonium bromide (CTAB), triterpenoid saponin (TS), sodium dodecylbenzenesulfonate (SDBS), sodium abietate (SA), cocamidopropyl betaine (CAB), and fatty alcohol polyoxyethylene ether (AEO-9)—were selected. Their foaming ability and time-dependent foam stability were measured in deionized water and in cement filtrate, and the air content of fresh mortars and the distribution of air-voids in hardened mortars were determined at 100 and 60 kPa. The results show that, at 100 kPa, TS, CAB, and CTAB produced higher initial foam height and better foam stability in deionized water than AEO-9, SA, and SDBS. TS and CAB also maintained a higher number density of bubbles and slower coalescence. In addition, all surfactant systems showed lower initial foam height and stability in cement filtrate than in deionized water, with SDBS, SA, and AEO-9 experiencing the greatest declines. When the pressure decreased from 100 kPa to 60 kPa, the mortar air content dropped by 8–15%, with the smallest reduction for TS (~8%) and the largest for CTAB (~15%). At 60 kPa, air voids with radius < 250 μm decreased markedly in hardened mortars: by 51%, 25%, and 28% for the control, CTAB, and AEO-9 mortars, respectively; but only by 14% for TS, highlighting its superior retention of fine air voids. Overall, amphoteric/saponin-type systems (represented by TS) exhibit better tolerance and stabilization, and are recommended for high-altitude concrete. Full article

Nanomaterials play a beneficial role in regulating the function of cement-based materials. The effects and mechanism of graphene oxide (GO) on foam behavior in solutions and air-entraining behavior of cement mortar were studied, and its effect on the microstructure of cement mortar was also investigated. The results show that a synergy between GO’s hydrophobicity and the air-entraining agent’s hydrophobic chains drove more agent molecules to adsorb onto the GO surface, subsequently spreading and aggregating across the bubbles. GO effectively assisted the air entraining agent to refine the bubble size, improved the bubble stability of aqueous solutions, and had excellent air entraining performance in the fresh cement mortar, as well as the optimum air-void adjustment performance of hardened cement mortars. With the addition of 0.4‰ GO, the loss rate of gas content in the GO mixed mortar was 10.3%, which was 55.8% lower than that when only using AEA. The addition of 0.4‰ of GO effectively increased the volume fraction of the cement mortar system. GO reduced the pore volume in the mortar through the filling effect and nucleation effect to reduce the total porosity and refine the microstructure of the mortar. Full article

The growing application of 3D concrete printing (3DCP) in construction has raised important questions regarding its long-term durability under freeze–thaw (F–T) exposure, particularly in cold climates. This review paper presents a comprehensive examination of recent research focused on the F–T performance of 3D-printed concrete (3DPC). Key material and process parameters influencing durability, such as print orientation, admixtures, and layer bonding, are critically evaluated. Experimental findings from mechanical, microstructural, and imaging studies are discussed, highlighting anisotropic vulnerabilities and the potential of advanced additives like nanofillers and air-entraining agents. Notably, air-entraining agents (AEA) reduced the compressive strength loss by 1.4–5.3% after exposure to F–T cycles compared to control samples. Additionally, horizontally cored specimens with AEA incorporated into their mixture design showed a 15% higher dynamic modulus after up to 300 F–T cycles. Furthermore, optimized printing parameters, such as reduced nozzle standoff distance and minimized printing time gap, reduced surface scaling by over 50%. The addition of a nanofiller such as nano zinc oxide in 3DPC can result in compressive strength retention rates exceeding 95% even after aggressive F–T cycling. The lack of standard testing protocols and the geometry dependence of degradation are emphasized as key research gaps. This review provides insights into optimizing mix designs and printing strategies to improve the F–T resistance of 3DPC, aiming to support its reliable implementation in cold-region infrastructure. Full article

Magnesium potassium phosphate cement (MKPC), a type of chemically bonded phosphate ceramic (CBPC), presents a promising alternative to ordinary Portland cement (OPC). This study focuses on developing sustainable MKPC (sust-MKPC) as a thermally passive material for building applications. A low-grade magnesium oxide (LG-MgO) industrial by-product was utilized to formulate sust-MKPC, with hydrogen peroxide employed as an air-entraining agent (AEA) to induce high porosity and enhance thermal insulation while supporting sustainability goals by reducing energy consumption in climate control systems. Seven formulations incorporating varying hydrogen peroxide contents (0, 1, 2, 3, 5, 7.5, and 10 wt.%) were prepared to evaluate the impact of AEA on the thermal and physicomechanical properties. Comprehensive characterization, including porosity and thermal conductivity measurements, revealed that increasing the AEA content significantly improved thermal inertia and lowered thermal conductivity due to porosity. However, this enhancement was accompanied by a marked reduction in mechanical strength and density, highlighting the trade-off between thermal performance and structural integrity in porous sust-MKPC formulations. Full article

This study systematically investigates the influence of mix proportion on and the early-age properties and CO₂ uptake of CO₂-mixed cement paste, focusing on variations in the water-to-binder (w/b) ratio, slag content, and air-entraining agent (AEA) dosage. Mineralogical characteristics were analyzed using X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while pore structures were assessed via nitrogen adsorption. CO₂ uptake was quantified immediately after mixing. Results indicate that a low w/b ratio limits CO₂ dissolution and transport, favors hydration over carbonation, and leads to a coarser pore structure. At moderate w/b ratios, excess free water facilitates concurrent carbonation and hydration; however, thinner water films ultimately hinder CaCO₃ precipitation and C-S-H nucleation. Slag contents up to 30% slightly suppress early carbonation and hydration, while higher dosages significantly delay both reactions and increase capillary porosity. An increasing AEA dosage stabilizes CO₂ bubbles, suppressing immediate CO₂ dissolution and reducing the early formation of carbonation and hydration products; excessive AEAs promotes bubble coalescence and results in an interconnected pore network. An optimized mix design, moderate water content, slag below 30%, and limited AEA dosage enhance the synergy between carbonation and hydration, improving early pore refinement and reaction kinetics. Full article

In the context of global energy scarcity, thermal insulation castables have garnered significant attention from the steel industry to reduce energy consumption. To optimize the performance of calcium hexaaluminate (CA₆)-based insulating castables, a systematic comparative study was conducted on the influence of varying amounts of calcium aluminate cement (CAC) incorporated into the castables. The results indicated that the addition of more CAC could increase the initial flowability of the castables with an air-entraining agent (AEA). Conversely, the flowability of the castables containing alumina bubbles continuously decreased after 30 min and 60 min. The apparent porosity of castables with only added AEA and alumina bubbles after being dried at 110 °C and treated at 1300 °C presented a decreasing trend as CAC content increased. Under the joint action of AEA and alumina bubbles, the amplification in porosity of castables treated at 1300 °C was positively correlated with the amount of CAC. The increase in CAC content could enhance the strength of samples, with a particularly notable improvement observed in castables prepared with the addition of AEA. For castables prepared with AEA and CAC contents of 9 wt.%, the cold modulus of rupture and cold crushing strength after heat treatment at 1300 °C were 17.5 MPa and 80.5 MPa, respectively. The thermal conductivity of castables presented non-monotonic change with the increase in CAC content. The effect of elevated CAC content on the pore fractal dimension of castables depended on the pore-forming methods. Grey correlation analysis (GCA) demonstrated that pore sizes in the range of 500–1000 nm, pore fractal dimensions, and pore sizes less than 500 nm had the highest degrees of correlation with CMOR, CCS, and thermal conductivity, respectively. Full article

Climate-change-induced extreme environments exacerbate pavement degradation in arid regions, where traditional concrete incurs 23~40% higher life-cycle costs due to premature cracking. Particularly in the Gobi Desert, concrete pavements suffer from conflicting performance requirements—high flexural-to-compressive strength ratio (R_f/R_c), low shrinkage, and controlled porosity—with traditional design methods failing to address multi-objective trade-offs. Existing optimization methods have proven insufficient for such complex environments, with conventional approaches addressing only individual parameters or employing subjective weighting techniques that fail to capture the interrelated nature of critical performance indicators. This study develops an integrated optimization framework combining Response Surface Methodology (RSM), Non-dominated Sorting Genetic Algorithm III (NSGA-III), Criteria Importance Through Intercriteria Correlation (CRITIC) weighting, and VIšekriterijumsko KOmpromisno Rangiranje (VIKOR) decision-making to optimize the mix proportions water–cement ratio (W/C), sand ratio, and an air-entraining agent (AEA) for sustainable pavement concrete. Response Surface Methodology (RSM) analysis via Box–Behnken design revealed distinct parameter dominance: AEA exhibited the strongest non-linear effects on R_f/R_c and porosity, while W/C primarily governed shrinkage. NSGA-III generated 73 Pareto-optimal solutions, with CRITIC selecting an optimal mix (W/C = 0.35), sand ratio = 36%, AEA = 0.200%) validated experimentally (R_f/R_c = 0.141), shrinkage = 0.0446%, porosity = 2.82%. Microstructural characterization using scanning electron microscopy and low-field nuclear magnetic resonance (SEM/LF-NMR) demonstrated refined pore distribution and enhanced compactness. This framework effectively resolves trade-offs between performance indicators, providing a scientifically robust method for designing durable pavement concrete that reduces shrinkage by 13.0% and porosity by 13.5% compared to conventional mixes, lowering maintenance costs in arid regions. Full article

Concrete quality is essential for highway guardrails in mountainous terrain to overcome freeze–thaw cycles, and manufactured sand (MS) concrete is potentially a more sustainable construction material. This paper aims to optimize the mechanical strength and freeze-thaw resistance of MS concrete for highway guardrails. The effects of water-to-binder (W/B) ratio (0.38–0.42), air-entraining agent (AEA) (0–0.5‱), fly ash (FA) (10–30%) and binder contents (360–380 kg/m³) on the properties of MS concrete were investigated. The mechanism behind the factors was further studied with scanning electron microscopy (SEM) and mercury injection porosimetry (MIP). Results showed that increasing W/B ratio, AEA and FA contents led to the reduction of compressive strength, but improved freeze–thaw resistance by reducing the mass loss during the cyclic freeze–thaw. SEM and MIP illustrated that the increase in W/B ratio and AEA addition increased the pore volume and caused a more porous structure, but increasing FA and binder contents densified the structure of MS concrete. This is consistent with the evolution of compressive strength and freeze–thaw resistance. This study offers an optimization method to obtain MS concrete with good compressive strength and freeze–thaw resistance for highway construction. Full article

Concrete is prone to cracking over time, leading to the deterioration of concrete structures. Using the biomineralization capabilities of bacteria, cracks in concrete can be remediated in favorable conditions. In this study, Bacillus subtilis spores were immobilized in three different healing agents, namely lightweight expanded clay aggregates (LECAs), polyvinyl acetate (PVA) fibers, and an air-entraining admixture (AEA). Bacillus subtilis spores, with a turbidity equivalent to a 4 McFarland standard, were used in three different dosages, namely 0.01, 0.1, and 1% (by weight) of cement. Based on the dosage, three groups were developed and each group consisted of a total of nine mixes, which were differentiated based on the method of delivery of the bacterial spores. The specimens were pre-cracked after 7 days, using an embedded steel rod, after being post-tensioned in a universal testing machine. The self-healing efficiency of the concrete was evaluated using ultrasonic pulse velocity testing and surface crack analysis, using ImageJ software, and the self-healing precipitate was analyzed using microstructural tests, namely scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis. The results verified that the self-healing efficiency of the concrete improved with the increase in the bacterial dosage and with an increase in the curing time. LECAs proved to be a promising bacterial carrier, by accommodating the spores and nutrient media over a period of 196 days. PVA fibers helped in bridging the cracks and provided nucleation sites for the bacteria, which enhanced the calcite precipitation. Similarly, the AEA also improved crack healing by encapsulating the spores and sealing cracks up to 0.25 mm, when used in conjunction with LECAs. Furthermore, microstructural tests verified the formation of calcite as a healing product within the cracks in the bioconcrete. The results of this study offer valuable insights for the construction industry, highlighting the ability of bacteria to reduce the deterioration of concrete structures and promoting a sustainable approach that minimizes the need for manual repairs, particularly in hard-to-reach areas. Full article

The use of superplasticizers in a self-compacting concrete mix without the addition of a foaming agent in practice leads to a well-known problem associated with increased air entrainment and promotes the formation of harmful large bubbles, high-void content, and ununiform appearance. This paper presents research on the properties of cement paste consisting of Ordinary Portland Cement (OPC), powder based on ground granulated blast furnace slag (GBBS), and superplasticizer. The methodology of this study was the estimation of flow diameter and flow time, as well as the evaluation of the rheological characteristics. The influence of ground granulated blast furnace slag and polycarboxylate plasticizer on the flowability and viscosity of cement paste was studied. The effect of superplasticizer (SP) based on polycarboxylate esters (PCE) anti-foaming agent (AFA) based on a glycol ester and air-entraining admixture (AEA) based on an amphoteric surfactant on flowability, viscosity, rheological properties and the strength of the cement paste was evaluated. It was found that the increase of slag content in cement paste (25%) with the presence of superplasticizer (0.64%) significantly changes the flowability and viscosity. It was stated that the addition of 0.04% anti-foaming agents increases flowability (20%) and reduces viscosity (44%) of cement paste. It was stated that the addition of small dosages of glycol ester-based anti-foaming agent (0.02 and 0.04%) significantly changes the rheological properties, decreases the shear yield stress by 2.1–2.8 times, the plastic viscosity by 2.4–2.6 times and apparent viscosity 1.6–2.5 times, improves the compressive strength at the age of 1 and 7 days by 2.5 and 1.4 times, respectively. The addition of air-entraining admixture led to a decrease in the plastic viscosity by 1.2–1.4 times. It was stated that the presence of air-entraining admixture assists in increasing the apparent viscosity by 1.7–2.4 times. It was shown that the presence of complex admixtures of various origins, purposes, and mechanisms of action would assist in predicting the behavior of concrete mixtures under the conditions of the building site and reduce the consumption of polycarboxylate esters due to the enhancing plasticizing effect of anti-foaming agent and air-entraining admixture. Full article

Clogging pipelines is one of the most common and urgent problems in paste backfill mining. The aim of the present study was to solve the problem of pipe blockage in paste backfill mining. In this paper, paste mixed with coal gangue, fly ash, cement, and additives is used to investigate the influence of three air-entraining agents (AEAs) (including sodium dodecyl sulfate (SDS), triterpene saponin (SJ), and sodium abietate (SA)) on the flow characteristics and strength characteristics of the paste. A series of relevant tests was conducted on the paste, such as air content experiments, slump and expansion experiments, viscosity and yield stress tests, and the uniaxial compressive strength (UCS) test. The results show that the air content of the paste increases with increasing AEA content, but the increase is limited and reaches a maximum at 0.9 AEA. The slump of the paste increased by up to 10–13 mm, and expansion increased by up to 66–130 mm compared to the paste without AEA. The viscosity of the paste decreased by up to 0.13–0.20 Pa·s, and the yield stress decreased by 81.47%–93.7% of the original. The strength of the paste was also reduced, and after 28 days of curing, the strength was reduced by up to 1–1.2 MPa. Taking into account the strength requirement of 3 MPa for the paste from the Linxi mine, it was considered that the dosage of 0.9 B was a good choice, as it could better change the flowability of the paste and reduce the pipeline transportation resistance and transportation energy consumption. At the same time, the strength was also acceptable. The study in this paper can provide a reference for performance studies of pastes mixed with coal gangue, fly ash, cement, and additives as materials. Full article

Three-dimensional concrete printing (3DCP) is becoming more common in the construction industry nowadays; however, the aspect of durability of printed concrete is not well-studied yet. Frost resistance is a very important factor for durability of concrete structures located in northern regions. Since air-entraining agents (AEAs) are widely used in conventional concrete, this paper focuses on exploring the potential of using AEAs in 3D concrete as well—the main objective is to determine how it affects fresh and hardened properties, including frost resistance of 3D concrete. Three different mixes were printed and cast—the dry mix consisted of ordinary Portland cement (OPC), limestone filler (LF), sand, as well as viscosity modifying agent (VMA) and superplasticizer (SP). Two mixes contained different amounts of AEA, the third one was used as reference. First, fresh state properties were tested—air content, density, and mini cone flow test. Second, 28-day compressive and flexural strength tests were carried out; bulk and particle densities were also determined. Next, both cast and printed concrete samples were subject to freeze–thaw cycles according to provisions of CEN/TS 12390-9, mass loss due to surface scaling was determined for each sample. As a result, printed concrete samples containing AEA in the amount of 0.06% of binder mass showed the highest frost resistance—addition of AEA decreased both flexural and compressive strength of this printed concrete mix by 30–40%. To conclude, the obtained results give an insight of how addition of AEA to printed concrete mix affects its properties both in long and short term. Further research of certain aspects, for instance, the air void system and pore distribution is needed to gain a deeper understanding on how to increase durability of 3D concrete. Full article

The utilization of waste crushed clay brick (CB) in concrete reduces its harmful impacts on the environment as it can be found in many places around the world. This research studies the possibility of using clay brick powder (CBP) as a filler material to produce lightweight concrete as it has been exposed to high temperatures during manufacturing of the bricks, which increases its pozzolanic reactivity. The effect of using an air-entraining agent (AEA) for additional pore formation on concrete performance was evaluated. Eight mixtures were prepared and examined to achieve the research objectives. Concrete flowability, dry density, compressive strength, ultrasonic pulse velocity, thermal conductivity, sorptivity, and porosity were measured. Additionally, scanning electron microscopy, X-ray diffraction, thermo-gravimetric analysis, and mercury intrusion porosimetry were used to analyze the microstructure characteristics of the concrete. The results indicate that the use of CBP as filler material enhances the mechanical and durability characteristics of the concrete. In contrast, adding an AEA has negative effects on concrete’s mechanical and durability properties, but on the other hand, its use enhances the thermal properties of the concrete. Full article

The efficiency and stability of air entrainment in concrete are sometimes found to be weaker at higher elevation. This phenomenon was attributed to the low atmospheric pressure by many researchers, however, the level of influence of atmospheric pressure on concrete air content dramatically varied among different studies. In order to clarify the effect of low atmospheric pressure on air entrainment in cement-based materials, an on-site experimental study was conducted with a rigorous control of irrelevant variables. The study focused on the air-entraining efficiency in cement paste, mortar, and concrete prepared in both low and standard atmospheric pressures. The air bubble stability in fresh mortar and air void characteristics of hardened mortar in different atmospheric pressures were also included. In the study, little effect of low atmospheric pressure on the air-entraining efficiency and air bubble stability in mortar with studied air-entraining agents (AEAs) was found. The air void characteristics were found to be similar between mortar with SJ-2 or 303R type AEAs prepared in different atmospheric pressures. Concrete with either SJ-2 or 303R type AEA prepared in low atmospheric pressure presented a satisfactory air content. These conclusions indicate that it is not necessary to worry excessively about the potentially adverse effect of atmospheric pressure on the frost resistance of concrete if a suitable AEA is applied. Additionally, a supplementary mortar study found that the low temperature of raw materials stored at high elevation would significantly weaken the air entrainment, reminding that potential causes in addition to low atmospheric pressure should also be taken seriously. Full article

At present, many mines adopt the filling method. It is particularly important to solve the problem of the long-distance transportation of slurry during the filling process. Based on the high-density filling material of Sanning mine, the experiments were designed to add sodium abietate (SA), triterpene saponin (SJ) and sodium dodecyl sulfonate (K₁₂) with concentrations of 0.0%, 0.2%, 0.4% and 0.6%, respectively, which were used as air entraining agents (AEA). The filling body with the curing age of 7 and 28 days was prepared for various tests, including nuclear magnetic resonance (NMR), and alternating current (AC) impedance tests. The effects of the air entraining agent and curing time on the physical properties, pore structure and AC impedance properties of the filling were obtained. The results show that: (1) within the frequency range of 10⁻¹–10⁵ Hz, the variation trend of AC impedance of the filling body cannot be changed by adding the air entraining agent, and the filling body with the same ratio had a similar topological structure. (2) The filling body with different AEA and curing times can be represented by the same equivalent circuit model, while the maximum chi-square coefficient was 0.46%. (3) Under the condition of a high frequency of 10⁵ Hz, the porosity and uniaxial compressive strength of the filling body with 7 day curing age were linearly correlated with the AC impedance. However, the porosity and uniaxial compressive strengths of the filling body with 28 days curing time were affected by the type of AEA at a high frequency of 10⁵ Hz. Full article