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To explore the mechanical properties of concrete under true triaxial static compressive load after sulfate attack, uniaxial static compression test and true triaxial static compression test at four stress ratios were carried out on concrete specimens immersed in 15% sulfate solution for 0–120 days by the integrated true triaxial static and dynamic load testing system, and the variation of performance indicators such as the strength and deformation of concrete under the coupling action of sulfate attack and complex stress state was analyzed. The results show that the uniaxial compressive strength of concrete increases at the beginning and then decreases with the increase of sulfate attack time and reaches the peak on the 30th day, with an increase rate of 16.57%; the strength of concrete under triaxial compression increases significantly, and the maximum triaxial compressive strength is 3.18 times of uniaxial compressive strength under the combination of 0-day sulfate attack and 0.2 : 0.8 stress ratio; and the deterioration of concrete under sulfate attack is more prominent at high confining pressure, and as the sulfate attack worsens, the sensitivity of triaxial compressive strength of concrete to lateral compressive stress is reduced. In conclusion, triaxial compression can significantly enhance the ductility of concrete by playing a role in restraining the deformation and cracking of concrete after sulfate attack.

The strength and deformation properties of carbon fiber reinforced concrete under different fiber volume loadings under impact loading were studied by using the ɸ100 mm split Hopkinson pressure bar (SHPB) test system. The results show that after the carbon fiber is added, the stress-strain curve of the specimen shows the platform section at the peak stress. The strength and peak strain of the concrete under the impact load increase first and then decrease with the increase of the carbon fiber volume. Trend, when the carbon fiber volume is 0.2%, the impact mechanical properties of concrete are significantly improved.

The formula describing the relationship between the dielectric constant of a composite and the dielectric constants or volume rates of its components is called a dielectric model. The establishment of a cement concrete dielectric model is the basic and key technique for applying electromagnetic wave technology to concrete structure quality testing and internal damage detection. To construct the dielectric model of carbon nanofiber reinforced concrete, the carbon nanofiber reinforced concrete was measured by the transmission and reflection method for dielectric constant &epsilon, and &epsilon, in the frequency range of 1.7~2.6 GHz as the fiber content was 0, 0.1%, 0.2%, 0.3% and 0.5%. Meanwhile, concrete was considered as a composite material composed of three phases, matrix (mortar), coarse aggregate (limestone gravel) and air, and the dielectric constants and volume rates of each component phase were tested. The Brown model, CRIM (Complex Refractive Index Model) model and Looyenga model commonly used in composite materials were modified based on the experimental data, suitable dielectric models of carbon nanofiber reinforced concrete were constructed, and a reliability check and error analysis of the modified models were carried out. The results showed that the goodness of fit between the calculated curves based on the three modified models and the measured curves was very high, the accuracy and applicability were very strong and the variation rule for the dielectric constant of carbon nanofiber concrete with the frequency of electromagnetic wave could be described accurately. For &epsilon, the error between the dielectric constant calculated by the three modified models and the corresponding measured values was very small. For the dielectric constant &epsilon, the average error was maintained below 1.2%, and the minimum error was only 0.35%, for the dielectric constant &epsilon, the average error was maintained below 3.55%.

This study experimentally examined the effect of redispersible polymer emulsion powder on dynamic compressive properties of carbon fiber-reinforced polymer concrete (CFRPC). Impact experiments of CFRPC cylindrical specimens (100 mm diameter, 50 mm height) with 0.2% carbon fiber (volume ratio of carbon fiber to concrete) to 0%, 4%, 8% and 12% polymer-cement ratios (mass ratios) were done using a Φ100 mm Split Hopkinson pressure bar. The effects of emulsion powder on CFRPC were analyzed in terms of the dynamic compressive strength, deformation and toughness of the specimens. We find that at the same strain rate, the dynamic compressive strength of CFRPC initially increases and then falls with increasing polymer content. The dynamic compressive strength of the sample is highest when the polymer-cement ratio is 4%, and reaches up to 21.47–26.58%. The compressive strength and peak strain of CFRPC have obvious strain rate sensitivity. An appropriate amount of polymer can effectively improve the dynamic compression performance of CFRPC. Sample fragmentation and porosity analyses show that increasing the polymer-cement ratio reduces the number of pores in the concrete matrix, attaining a more optimal pore distribution and improved compactness.

This study examined the tensile and fixed elongation properties of flexible composite made of styrene&ndash, acrylic, vinyl acetate-ethylene copolymer emulsion (VAE emulsion), and cement as cementitious material for airport pavement joint sealant. Quantitative analysis of the elastic recovery ratio and a series of specimen tensile indicators after water immersion, drying&ndash, wetting cycles, and corrosive solution (H2SO4, NaOH, and jet fuel) immersion were performed. Results showed excellent polymer-based cement flexible composite (PCFC) resistance against water and corrosive solution erosion, such as failure mode, elastic recovery, tensile strength, and energy absorption. When the level of water/corrosive solution erosion (immersion time, cycles) were increased, the tensile and fixed elongation properties progressively decreased. Specimens retained more than 60% elastic recovery ratio after water/corrosive solution erosion immersion for 30 days. According to erosion testing as per immersion time in corrosive solution, jet fuel had the maximum effect, NaOH solution had the least effect, and H2SO4 solution had an intermediary effect. At immersion time in the range of 1&ndash, 30 days, the tensile strength does not change by more than 0.07 MPa. Within the limits of the fixed elongation tests, cohesive failure occurred after jet fuel immersion for 30 days, adhesive failure occurred after H2SO4 solution immersion for 30 days but was normal in other cases.

To study the effect of redispersible polymer emulsion powder on the mechanical properties of carbon fiber-reinforced polymer concrete (CFRPC), the compressive, flexural, and splitting tests of CFRPC specimens with different polymer&ndash, cement ratios (polymer&ndash, cement mass ratios) were performed in this study. The modification effect of emulsion powder on CFRPC was analyzed from the perspectives of the strength and deformation properties of the specimens. The results show that the static properties of CFRPC increased first and then decreased with the increase of the polymer&ndash, cement ratio, in which the splitting tensile strength had the most significant increase, the flexural strength took second place and the compressive strength had a slight increase. When the polymer&ndash, cement ratio was 8%, the flexural and splitting tensile strength of the CFRPC specimens increased significantly by 36% and 61%, respectively. According to electron microscopy images, adding emulsion powder can effectively improve the structure of fiber&ndash, matrix transition zones and enhance the bond property between fibers and the matrix.

To study the effect of carbon nanofibers (CNFs) on the electrical conductivity of concrete, we used the four-electrode method to measure the resistance and resistivity of carbon nanofiber reinforced concrete (CNFRC) under different ages, different fiber content and different test voltages. The results show that the incorporation of CNFs into concrete can improve the electrical conductivity of concrete. The electrical resistance and electrical resistivity of CNFRC increase with the increase of concrete age, but the growth rate decreases gradually. The resistance and electrical resistivity of CNFRC decrease with the increase of carbon nanofiber content and the optimum dosage range is 0.1%-0.3%. The resistance and electrical resistivity of CNFRC decrease with the increase of test voltage, and when the test voltage is 1V~5V, the resistance and electrical resistivity decrease significantly.

To study on the toughing effect of EPS in the plain concrete, the EPS concrete with 10%,20%,30%,40%,50% EPS volume fraction were prepared. Taking specific energy absorption as the index, the toughing effect of EPS concrete with different EPS volume fraction under impact loading were studied using a 100-mm-diameter split Hopkinson pressure bar(SHPB) apparatus, and the toughing effect mechanism of the concrete was discussed. The results show that the toughing effect of the EPS concrete increases with the average strain rate for the strain rate effect, which takes on obvious strain rate dependency. For the EPS microscopic structure effect, the toughing effect of the EPS concrete increases with the EPS volume fraction in 10~30%. Its toughing effect reduces somewhat when the EPS volume fraction reaches 40~50%. To improve the deformation property, the optimum volume fraction of EPS is 20%.

The EPS concrete with 10%，20%，30%，40%，50% EPS volume fraction were prepared. Taking critical strain as the index, the deformation property of EPS concrete with different EPS volume fraction under impact loading were studied using a 100-mm-diameter split Hopkinson pressure bar(SHPB) apparatus. The results show that the deformation property of the EPS concrete increases with the average strain rate for the strain rate effect, which takes on obvious strain rate dependency. For the EPS microscopic structure effect, the deformation property of the EPS concrete increases with the EPS volume fraction in 0~40%. Its deformation property reduces somewhat when the EPS volume fraction reaches 50%. To improve the deformation property, the optimum volume fraction of EPS is 40%.

In this paper, in order to investigate impact-mechanics property of basalt fiber reinforced concrete (BFRC), impact test on BFRC with four kind of volume content (0, 0.1%, 0.2, 0.3%) was carried out using 100mm-diameter split hopkinson pressure bar (SHPB) device. Obtained dynamic stress-strain curves and testing data. Testing results were analyzed. The testing results showed that BFRC has favorable impact-mechanics properties, strain rate and fiber volume content have large effects on impact-compression strength and toughness of BFRC; impact-compression strength and toughness show strain rate strengthening effect, strain rate sensitivity of impact-compression strength is stronger and the impact-compression strength and toughness are higher relatively when fiber volume content is 0.1%; there is approximate linear function relation between the dynamic strength increase factor and the strain rate logarithm, there is approximate quadratic polynomial function relation between the peak strain and the strain rate logarithm.

Because of the facts of reinforced concrete structures materials and used environment, very severe durability problems occurred in reinforced concrete structures. Research on reinforced concrete structures durability has become one of the world-wide concern problems in structural engineering. Extension method based on matter-element theory and conjunction function is introduced to evaluate durability of reinforced concrete structures in this paper. The matter-element model for durability evaluation of reinforced concrete structures is established by chose seven evaluation indexes. Applying simple conjunction function to calculate the weight coefficient of evaluation indexes can reduce the error caused by subjective judgment, and makes the results more objective. The research indicates that extension method is reasonable and feasible in evaluating durability of reinforced concrete structures.