Relative Dynamic Elastic Modulus Research Articles

Effect of Freeze–Thaw Cycles on the Performance of Concrete Containing Water-Cooled and Air-Cooled Slag

An experimental study on the resistance of concrete containing air-cooled slag (AS) and water-cooled slag (WS) against freeze–thaw cycles was conducted. For comparison, the durability of ASTM Type I ordinary Portland cement (OPC) concrete exposed to the same freeze–thaw environment was examined. To evaluate the durability of concrete exposed to the freeze–thaw environment, an experiment was conducted according to ASTM C 666 procedure A. Furthermore, the relative dynamic modulus of elasticity, surface electrical resistivity, and compressive strength of concrete specimens were measured after exposing them to freeze–thaw cycles for a predetermined period, and the results were compared with those of OPC concrete. The relationship between the freeze and thaw resistances of concrete and the air-void system (spacing factor and specific surface area) was identified. Furthermore, the microstructure of concrete exposed to freeze–thaw cycles was observed using scanning electron microscopy to identify the interfacial transition zone, cracks, and micropores. Experimental results showed that the resistance of blended cement concrete containing WS and AS against freeze–thaw cycles was significantly higher than that of OPC concrete. The concrete in which 10% of OPC was replaced by AS exhibited a similar durability as that of the concrete in which 40% of OPC was replaced only by WS. Therefore, it is expected that blended cement concrete containing WS and AS based on an appropriate mix proportion design will exhibit excellent durability in regions experiencing freezing temperatures.

Effect of basalt fiber on the freeze-thaw resistance of recycled aggregate concrete

Recycled aggregate concrete (RAC) is considered a good way of sustainable development, but compared with natural coarse aggregates (NCA), the performance of recycled coarse aggregates (RCA) is often worse. This study aimed at the basalt fiber (BF) enhances the frost resistance of RAC. Therefore, a rapid freeze-thaw cycles test was carried out on basalt fiber reinforced recycled aggregate concrete (BFRRC), with the variation of three different replacement ratios of RCA (i.e., 0, 50 and 100%) and four different contents of BF (i.e., 0, 2, 4 and 6 kg/m3). Then, the damage appearance, mass losses, and relative dynamic elastic modulus (RDEM) of specimens were analyzed. Results were showed that the appearance damage characteristics of RAC are different from NAC, as the replacement ratio of RCA was increased, the damage appearance of the specimens was exacerbated, and surface spalling transformed into corner spalling and holes were generated in the surfaces of the specimens. Compared with mass loss, REDM can better reflect the frost resistance of BFRRC. BF could significantly improve the damage appearance and RDEM loss of the specimens, incorporating 4 kg/m3 of BF can significantly improve the frost resistance of RAC. In addition, the mechanism of freeze–thaw damage was revealed by using scanning electron microscopy (SEM) and damage theory, a freeze–thaw damage model of BFRRC was established by defining the damage degree on the basis of the RDEM. The results of this work could provide a reference for the further research and engineering application of BFRRC.

Effect of steel fiber on impact resistance and durability of concrete containing nano-SiO2

Abstract Impact drop weight tests, rapid chloride migration coefficient tests, single-sided freeze–thaw tests, and mechanical property tests were performed to investigate the effect of the steel fiber (SF) content on the impact resistance and durability of concrete containing nano-SiO2 (NS). A fixed NS content of 3% and six SF contents in a range of 0–2.5% by volume were used. The impact resistance was measured based on the number of blows (N1, N2) and the impact energy. The durability of concrete includes its freeze–thaw resistance and chloride ion penetration resistance, which were appraised by the chloride ion diffusion coefficient (CDC) and relative dynamic elastic modulus (RDM), respectively. The ductility ratio was used to predict the impact resistance of concrete containing NS with different SF contents, and a linear relation between this ratio and the impact energy (R 2 = 0.853) was found. The experimental results indicated that SF could greatly improve the impact resistance of concrete. The addition of 2.0% SF increased N1 and N2 by 106 and 169%, respectively. In addition, an appropriate SF content significantly improved the durability of the concrete, including its frost resistance (especially in the middle and late freezing–thawing cycles) and chloride ion penetration resistance. An SF content of 1.5% was the optimum, decreasing the CDC of nano-concrete by 17.1% and minimizing the RDM loss. Moreover, the 1.5% SF content increased the compressive strength of concrete containing NS by 18.5%, whereas an SF content of 2.0% increased the splitting tensile strength and flexural strength by 77 and 20%, respectively. Furthermore, when the SF content exceeded a certain value, the improvement effect on these properties began to decrease and even became negative.

Aggressive Environment Resistance of Concrete Products Modified With Nano Alumina and Nano Silica

The service life of concrete products with exposure to an aggressive environment has raised great concerns in the past decades. Nanomaterials have been used as a promising approach to improve the environmental resistance of concrete products when exposed to synergistic attacks. The impacts of CaCl2 on nano-modified concrete, especially along with freeze/thaw (F/T) and wet/dry (W/D) cycles, were barely discussed. In this study, the impacts of CaCl2 along with F/T and W/D cycles on the nano SiO2 and Al2O3 modified concrete were investigated. The mass loss, flexural strength, compressive strength, and relative dynamic modulus of elasticity were tested to evaluate the durability of concrete products. The testing results indicate that the addition of nanoparticles has a distinctive effect on the environment resistance enhancement of concrete samples. The microstructure analysis demonstrates that with the addition of nanoparticles, high-density hydration products were formed, which is beneficial to the properties enhancement of concrete products. This study not only provides an approach to realize the nano modification on the durability of concrete products but also helps to design and fabricate environmentally resistant concrete products when exposed to a synergistic aggressive environment.

Experimental study on sulfate erosion resistance of nano-CaCO3 modified concrete

In the saline soil environment of western China, salts can corrode ordinary cement concrete seriously, and the durability of concrete structure deteriorates gradually until it fails. This impedes the application of ordinary Portland cement concrete in this area. Aiming at the problem of the short service life of concrete in the harsh environment of western China, this study examines the performance of nano-CaCO3 modified concrete in a sulfate environment. The durability of the concrete was evaluated by the apparent phenomena on the relative quality evaluation parameter, the relative dynamic elastic modulus evaluation parameter, and the comprehensive damage evaluation parameter. The microstructure of corroded products was investigated using scanning electron microscopy to reveal the deterioration mechanism. The results show that the addition of 1% nano-CaCO3 can enhance the resistance of concrete to sulfate corrosion, and the service life of concrete structures will increase significantly.

Effect of freeze–thaw cycling on mechanical properties of polyethylene fiber and steel fiber reinforced concrete

This paper experimentally studied the influence of freeze–thaw cycles on the mechanical property of hybrid PE and steel fiber reinforced concretes (FRC). Five different FRC mixtures and a reference mixture were prepared for the comparative study. After 250 freeze–thaw cycles, the tension, compression, bending and fracture tests all showed that freeze–thaw cycles have minimal effect on the strength but significant influence on the deformability of FRCs. Analysis on relative dynamic modulus of elasticity and mass loss ratio indicated that the high compactness of matrix maintains the matrix integrity and thus keeps strength stability. Single fiber pull-out tests revealed the variations of peak strength and the corresponding displacement when fiber is pulled out of matrix before and after freeze–thaw treatment. It is demonstrated that freeze–thaw cycles impair the fiber/matrix interfacial bond, which is attributed to be the main cause to the degradation of deformability.

Effect of Nano Silica Particles on Impact Resistance and Durability of Concrete Containing Coal Fly Ash.

In this study, the effect of adding nano-silica (NS) particles on the properties of concrete containing coal fly ash were explored, including the mechanical properties, impact resistance, chloride penetration resistance, and freezing–thawing resistance. The NS particles were added into the concrete at 1%, 2%, 3%, 4%, and 5% of the binder weight. The behavior under an impact load was measured using a drop weight impact method, and the number of blows and impact energy difference was used to assess the impact resistance of the specimens. The durability of the concrete includes its chloride penetration and freezing–thawing resistance; these were calculated based on the chloride diffusion coefficient and relative dynamic elastic modulus (RDEM) of the samples after the freezing–thawing cycles, respectively. The experimental results showed that the addition of NS can considerably improve the mechanical properties of concrete, along with its freezing–thawing resistance and chloride penetration resistance. When NS particles were added at different replacement levels, the compressive, flexural, and splitting tensile strengths of the specimens were increased by 15.5%, 27.3%, and 19%, respectively, as compared with a control concrete. The addition of NS enhanced the impact resistance of the concrete, although the brittleness characteristics of the concrete did not change. When the content of the NS particles was 2%, the number of first crack impacts reached a maximum of 37, 23.3% higher compared with the control concrete. Simultaneously, the chloride penetration resistance and freezing–thawing resistance of the samples increased dramatically. The optimal level of cement replacement by NS in concrete for achieving the best impact resistance and durability was 2–3 wt%. It was found that when the percentage of the NS in the cement paste was excessively high, the improvement from adding NS to the properties of the concrete were reduced, and could even lead to negative impacts on the impact resistance and durability of the concrete.

Life Prediction Model of Nano-CaCO3 Modified Concrete in Sulfate Environment

In the saline soil environment, the salts corrode the ordinary cement concrete seriously, and concrete structures deteriorate gradually until it fails, which impedes the practical application of ordinary Portland cement concrete in this area. Aiming at the durability problems of concrete in a harsh environment, this paper selects the coefficient of compressive strength, coefficient of flexural strength, relative dynamic elastic modulus, and relative mass to jointly evaluate the resistance of nano-CaCO3 modified concrete to sulfate corrosion. More importantly, the Wiener process for modeling the degradation process of concrete specimens was used to obtain the remaining life’s reliability function. The results indicated that adding 1% nano-CaCO3 (Nano Calcium Carbonate) can enhance the resistance of concrete to sulfate corrosion, and the service life of concrete will increase significantly. The Random Wiener process can effectively predict the durability deterioration process of concrete specimens. By integrating the deterioration process’s life data, this method’s reliability function may directly reflect the concrete’s life.

17-Year-Long Sewage Sludge Ash Concrete Exposure Test

This study was conducted on concrete using sewage sludge ash (SSA) with the aim to establish an efficient use of SSA as a cement replacement material. Concrete specimens with three degrees of strength were made from two different SSAs and exposed in temperate plain and cold mountain regions for a prolonged period of time to investigate the long-term properties of SSA concrete. After 17 years of exposure, the properties of the specimens were examined. SSA concrete basically maintained its strength after 17 years of exposure. No significant drop in the relative dynamic modulus of elasticity was detected in SSA concrete left in a cold mountain region, despite the fact that it would be exposed to a considerable number of freeze-and-thaw cycles. It was also confirmed that the SSA concrete exhibited high resistance against carbonation. A small amount of Katoite formed in the hardened cement/SSA mixture, probably due to the high content of Al2O3 in SSA. No abnormal formation of ettringite was observed.

Mechanical Properties and Damage Evolution of Concrete Materials Considering Sulfate Attack.

In order to study the durability of concrete materials subjected to sulfate attack, in a sulfate attack environment, a series of concrete tests considering different fly ash contents and erosion times were conducted. The mechanical properties and the micro-structure of concrete under sulfate attack were studied based on the following: uniaxial compressive strength test, split tensile test, ultrasonic impulse method, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties were compressive strength, splitting tensile strength, and relative dynamic elastic modulus, respectively. Additionally, according to the damage mechanical theory, experimental results and micro-structure analysis, the damage evolution process of concrete under a sulfate attack environment were studied in detail. Finally, according to the sulfate attack time and fly ash content, a damage model of the sulfate attack of the binary surface was established. The specific results are as follows: under the action of sulfate attack, the change law of the rate of mass change, relative dynamic modulus of elasticity, corrosion resistance coefficient of compressive strength, and the corrosion resistance coefficient of the splitting tensile strength of concrete all increase first and then decrease. Under the same erosion time, concrete mixed with 10% fly ash content has the best sulfate resistance. Through data regression, the damage evolution equation of the sulfate attack was developed and there is an exponential function relationship among the different damage variables. The binary curved surface regression effect of the concrete damage and the erosion time and the amount of fly ash is significant, which can predict deterioration of concrete damage under sulfate attack. During the erosion time, the combined expansion of ettringite and gypsum caused micro cracks. With an increase of corrosion time, micro cracks developed and their numbers increased.

Texture analysis of the microstructure of concrete with different concentrations of superabsorbent polymer after internal curing

Internal curing has been widely used in high-strength concrete because it can replenish water for cement hydration and reduce self-shrinkage. The internal curing effects mostly depend on the self-shrinkage changes and mechanical parameters obtained through a destructive test. This research proposes a fast and nondestructive detection method based on image recognition analysis to determine the effects of internal curing material content on the performance of high-strength concrete. The superabsorbent polymer (SAP) was chosen as the internal curing material. Laboratory uniaxial compression tests, scanning electron microscopy (SEM), and energy dispersive spectroscopy were used to analyze the mechanical properties and phase characteristics of the concrete. Based on the SEM images, the gray level co-occurrence matrix was used to extract texture features of the concrete, and effective SEM image samples were screened out to verify the correlation between texture features and mechanical strength. The results showed that: (1) the four characteristic values of GLCM have a significant linear correlation with SAP content; (2) with the increase in SAP content, self-shrinkage decreases and reaches the smallest point when the SAP content is 0.24 % of the cementing material content; and (3) the relative dynamic modulus of elasticity and maximum shrinkage are negatively correlated with the energy and correlation and positively correlated with the contrast and entropy. Such results provide a simple method of determining the influence of internal curing content on concrete performance.

Influence of Limestone Powder and Fly Ash on the Freezing and Thawing Resistance of Roller-Compacted Concrete

Roller-compacted concrete (RCC) comprises the same raw materials used in conventional concrete, but with different proportions. It is dry and has a low paste volume. Large volumes of fly ash are commonly used in the construction of roller-compacted concrete dams (RCCD) and pavements (RCCP). However, it is not as abundant as limestone powder. The latter is also cheaper and environment-friendly. This study aims to investigate the optimal amount of limestone powder that can be used in RCC to reduce both cement and fly ash. The effects of limestone powder and fly ash on the water absorption, compressive strength, and freeze-thaw resistance of RCC were evaluated. Eight different combinations of the mineral admixtures were tested, with limestone powder and fly ash contents up to 35% and 30%, respectively. A decline in density was observed when the cement replacement level was greater than 30%. This also led to an increase in porosity and permeability. Two mix designs denoted as LS30 and LS30FA10, demonstrated satisfactory results after 100 freeze-thaw cycles with relative dynamic modulus of elasticity (RDME) values of 73% and 70%, respectively. Their corresponding mass loss was 3.05% and 3.72%, which were below the code specified limit (5%).

DURABILITY PROPERTIES OF RECYCLED CONCRETE WITH LITHIUM SLAG UNDER FREEZE-THAW CYCLES

A water freeze-thaw cycle and sulfate freeze-thaw coupling cycle were explored experimentally to evaluate the durability of recycled concrete with lithium slag (LS). The damage-deterioration law was studied from the aspects of mass-change rate, relative dynamic modulus of elasticity, and cube’s compressive strength. Based on the relative dynamic modulus of elasticity, the damage-degree equation of the concrete was fitted, and a mechanical-attenuation model related to this parameter and the cube’s compressive strength was established and verified. The damage mechanism under the action of the sulfate freeze-thaw cycle was revealed through scanning electron microscopy (SEM). The combination of recycled coarse aggregate (RCA) and LS was beneficial to the anti-deterioration ability of the concrete. During the cycle experiments, the mass and relative dynamic modulus of elasticity increased initially and then decreased, while the cube’s compressive strength declined continually. The concrete with a 30 % RCA substitution rate and 20 % LS exhibited the optimal comprehensive durability, and specimens with excessive LS showed more susceptibility to sulfate erosion. The residual compressive strength of concrete structures can be evaluated by measuring the relative dynamic modulus of elasticity as the two parameters are ideally correlated.

Sulfate attack resistance of recycled aggregate concrete with NaOH-solution-treated crumb rubber

This study investigates the sulfate attack resistance of recycled aggregate concrete with NaOH-solution-treated crumb rubber (CR). For this purpose, several recycled aggregate concrete mixes were developed using different concentrations (10%, 20% and 30%) of NaOH-solution-treated CR and different CR particle sizes (0.16–0.3 mm, 0.85–2 mm and 10–20 mm). The performance, including mass loss, residual compressive strength, relative dynamic modulus of elasticity (RDME) and microstructure, was evaluated in the sulfate environment. Results reveal that the macroscopic performance of recycled aggregate concrete with CR presents three stages: the early enhancement or slow declining stage, middle declining stage and subsequent accelerated declining stage. The addition of CR particles could improve the sulfate attack resistance of recycled aggregate concrete, and the effect was more significant for the NaOH-solution-treated CR particles than for the untreated CR. Moreover, 0.16–0.3 mm CR particles and 20% NaOH solution pretreatment were the optimum conditions in this assessment range to enhance the sulfate attack resistance. Although the surface scaling tended to worsen in recycled aggregate concrete mixtures with 10–20 mm CR due to its weaker mortars, the mixtures were still durable in sulfate attack conditions owing to their higher residual RDME and compressive strength than those of recycled aggregate concrete. The results of the analysis of corrosion products through X-ray diffraction and the microstructure through scanning electron microscopy are consistent with the macroscopic performance.

The Influence of Fair-Faced Concrete Protective Agent on the Resistance to Freezing and Thawing of Concrete

Protective agents can effectively improve the weather resistance of fair-faced concrete. The surface of C40 concrete is treated with acrylic acid, silicone and fluorocarbon fair-faced concrete protectors respectively. Five groups of tests are carried out and forty-eight specimens are used. The effect of different coating layers on the resistance to freezing and thawing of concrete are systematically studied and compared with the standard test block that is not painted with the fair-faced concrete protector. The results indicate: the anti-freezing ability of topcoat is greater than that of the primer; in the aspect of different protectors, fluorocarbon has the best effect, silicon takes the second, and acrylic acid has the worst effect; with the increase of the number of protective agents, the anti-freezing ability of the concrete specimen is gradually improved; in consideration of economy and durability, two coats of primer and two coats of topcoat have the best effect. When the freeze-thaw cycle reaches 150 times, the relative dynamic elastic modulus of the test pieces coated with the fluorocarbon, silicone and acrylic acid fair-faced concrete protectant systems are 83.3%, 80.4%, and 72.9%, respectively.

Frost Resistance and Pore Structure of Concrete Incorporated with Rubber Aggregates and Nano-SiO2.

This paper aims to develop frost-resistant concretes, and investigate their pore structures and freeze–thaw damage mechanism. The frost-resistant concrete mixtures are designed by using rubber particles and nano-SiO2 to partially replace sands. The chord lengths, specific surface areas, contents and spacing coefficients of the pores in the designed concretes are measured and analyzed. The results show that concrete mixture incorporated with 5% silanized rubber and 3% nanosilica shows good synergetic effect by considering both mass loss and relative dynamic modulus of elasticity (RDME). The freeze–thaw damage degree of the concrete could be reduced by adding high elastic rubber particles, due to filling and constraining pores, and resulting in better uniform pore distribution and smaller pore spacing coefficient. Furthermore, the correlations between frost resistance and pore are analyzed and proposed.

Assessing the Effects of Steelmaking Slag Powder on the Pore Structure and Durability of Concrete

This study analyzes the pore structure and durability of concrete according to four different ratios of steelmaking slag powder (SSP). Concrete containing SSP increased the formation of gel and capillary pores due to delayed hydration, and the largest cumulative pore volume was observed when the incorporation ratio was 20%. In terms of durability, the incorporation of SSP had decreased performance compared to concrete without SSP (NN), which was due to changes in the pore structure caused by incorporating SSP. In the case of the freezing and thawing resistance, concrete containing 10% SSP showed a remarkable relative dynamic elastic modulus of more than 80%, and a similar carbonation depth was predicted within 15% of SSP. In addition, the resistance performance of chloride ion migration in concrete with SSP was excellent. Accordingly, it can be utilized as a supplementary cementitious material if the freezing and thawing resistance of concrete containing 15% SSP is secured.

Influence of Old Concrete Age, Interface Roughness and Freeze-Thawing Attack on New-to-Old Concrete Structure.

The bonding surface structure generated by the repair of concrete structures has been paid more attention as a weak point. The effects of old concrete age, interface roughness, and freeze-thawing (F-T) attack on adhesive interface are comprehensively investigated. In this study, six kinds of interface roughness and five different old concrete age are designed. The interfacial bonding property is mainly evaluated by splitting tensile strength (fts). Fractal analysis was used to characterize the interface roughness using laser scanning data. In general, the fts increased with the increasing value of interface fractal dimension. The relationship between fts and fractal dimension value was further analyzed, considering the old concrete ages and the F-T cycles. The results show that the effect of roughness on the bonding property of new-to-old concrete is more significant than the age of old concrete, and the influence of the F-T cycles on the bonding surface is mainly reflected in the initial stage of the F-T deterioration process. The relative dynamic elasticity modulus decreased obviously under F-T cycles, especially for the specimens with low interface roughness. In combination with the results of two non-destructive methods (ultrasonic non-destructive test and relative dynamic elastic modulus test), the larger roughness and the smaller age of old concrete can improve the bond performance.

Effect of Different Mineral Admixtures on the Properties of Pervious Concrete

Taking pervious concrete with a target porosity of 15% as the research object, the influence of three factors, including the contents of silica fume (mass fraction3%, 5%, 7%), metakaolin (mass fraction8%, 10%, 12%) and Polypropylene fiber content (volume fraction1%, 2%, 3%), on the mechanical properties, permeability and frost durability of pervious concrete were investigated by utilizing the orthogonal testing method. Through the range analysis of the test results, the significant influence degree of the three factors were obtained, and the freeze-thaw cycle test was carried out with the optimal mix ratio. The results indicated that the content of silica fume and metakaolin has the most significant influence on the mechanical properties of pervious concrete, the fiber has the most significant influence on the continuous porosity, but the influence on the compressive strength is small. The best mix proportion was obtained, and the silica fume content is 7%, metakaolin content is 10%, and fiber content is 2%. The results of freeze-thaw cycle test of pervious concrete with optimal mix ratio show that the relative dynamic modulus and compressive strength of pervious concrete decrease gradually with the increase of freezing-thawing cycles, and the change rate of mass loss, continuous porosity increases gradually with the increase of freeze-thaw cycles. The relative residual compressive strength and dynamic elastic modulus of pervious concrete show a parabolic decline trend subjected to freeze-thaw cycles. The results also can provide technical reference for the engineering application of pervious concrete in cold regions.

Freeze-thaw Durability of Recycled Aggregate Concrete: An Overview

The characteristics of surface appearances, mass loss, relative dynamic modulus of elasticity and strength loss of different recycled aggregate concretes(RAC) exposed to freeze-thaw cycles were analyzed. It was found that the freeze-thaw resistance of RAC could be determined by the recycled aggregate compositions and admixtures. Both the saturation degree and the air void structure were the key factors influencing the freeze-thaw damage on concrete. Some major proposed freeze-thaw deterioration mechanisms were utilized to interpret the freeze-thaw damage on recycled aggregate concrete. Meanwhile, some potential measures to enhance the freeze-thaw resistance of concrete were summarized and discussed.