Addition Of Air-entraining Agent Research Articles

Study on microstructure of cemented paste backfill with initial defects under uniaxial compression failure

In order to fully understand the micro and fine structural characteristics of the cemented paste backfill (CPB) with initial defects, this paper carries out uniaxial compression test on the CPB and real-time monitoring with DIC technology, analyses the crack extension and deformation characteristics on the surface of the specimen, carries out SEM test on the damaged specimen, binarizes the SEM images, and performs microscopic pore analysis on the processed binarized images using PCAS software. Then some parameters such as porosity, probability entropy, probability distribution index, fractal dimension, form factor, etc. of the specimens with different initial defects are discussed. The study shows that the damage form of CPB under uniaxial compression is mainly tensile damage, and gradually changes from tensile damage to shear damage when the specimen reaches the peak strength. The overall displacement and strain of each monitoring point on the specimen increases rapidly after entering the plastic deformation stage. There are many small microcracks and pores in the CPB, and there are a large number of aciculate ettringite and C-S-H gel hydration products, which are generated in the sample unevenly. With the addition of air-entraining agent (AEA), within a certain range, the number of pores inside the CPB increases. Many small pores also form large pores because of the connectivity between the pores, the porosity of the specimen increases, and the morphology and structure of the pores are relatively more regular. However, the direction of the pore development still does not have good directionality, and the initial defects become increasingly obvious.

Air void system and freezing-thawing resistance of concrete composite with the incorporation of thermo-expansive polymeric microspheres

Air-entraining agent (AEA) was first used in concrete in 1930’s to improve freezing – thawing resistance of concrete. After about 90 years of experience, many debates have been raised regarding the benefit of durability improvement using AEA in concrete. Under this circumstance, polymeric microspheres show promising ability to replace the AEA with the purpose of entraining air in concrete. In this study, thermo-expansive polymeric microspheres were added to concrete. As a comparison, concrete specimens with the addition of AEA were also prepared. The air contents of freshly mixed concrete and hardened concrete were characterized. In addition, compressive strength development was measured. Moreover, the microstructure and air-void system of concrete was characterized by multiple methods. Finally, the dynamic modulus of elasticity and scaling of concrete beams after the cyclic freezing–thawing attack were evaluated. It was found that compared with the addition of AEA, adding polymeric microspheres entrained comparable air content in concrete. The void size distribution of polymeric microspheres mixed concrete is finer than that of AEA mixed concrete, which provides comparable freezing–thawing resistance of concrete in the viewpoint of dynamic modulus. However, due to the potential “internal curing” and nucleation effects with the presence of microspheres, the strength of microsphere-mixed concrete is slightly higher than that of plain concrete, and freezing–thawing caused surface scaling of concrete mixed with microspheres is much less severe than that incorporated with AEA.

Effects of air-entraining agent and polypropylene fiber on the mechanical properties, autogenous shrinkage, and fracture properties of fully recycled aggregate concrete

The effects of air-entraining agent (AEA) and polypropylene fiber (PPF) on the autogenous shrinkage and fracture properties of fully recycled aggregate concrete (FRAC) are studied to obtain FRAC with low density, low autogenous shrinkage, and superior fracture properties. Six groups of FRAC with different AEA (0, 5%, 10%) and PPF (0, 1.2 kg/m3) contents were prepared for test. The results illustrate that AEA can slightly reduce density but that it has an adverse effect on the strength and fracture properties of FRAC. The incorporation of PPFs can reduce the adverse effect of AEA on compressive strength and splitting tensile strength, but it will increase the adverse effect on fracture properties. Furthermore, the addition of PPFs alone will significantly reduce compressive strength and splitting tensile strength, whereas flexural strength and fracture properties are increased. The addition of AEA can improve the adverse effect of PPFs on compressive strength and splitting tensile strength, but flexural strength and fracture properties will decrease rather than increase. The addition of 10% AEA can greatly reduce autogenous shrinkage, and 5% AEA can reduce autogenous shrinkage at an early age. Incorporating PPFs can further reduce autogenous shrinkage. The study mainly examines the effects of AEA and PPF on the autogenous shrinkage of FRAC, and provides some new ideas for producing high-performance FRAC. At the same time, the cooperative effect of AEA and PPF on the properties of FRAC is also studied.

Mechanical and Damping Properties of Recycled Aggregate Concrete Modified with Air-Entraining Agent and Polypropylene Fiber.

In this study, recycled aggregate concrete (RAC) modified with polypropylene fiber (PP) and air-entraining agent (AGA) was prepared, and the effects of PP and AGA on the static (compressive strength, Young’s modulus, and splitting tensile strength) and dynamic properties (dynamic modulus of elasticity and damping ratio) of RAC were investigated. The experimental results showed that the addition of an AGA and PP had a favorable effect on the damping ratio of the concrete, however, the addition of the AGA had a slightly negative effect on the mechanical performance of the concrete. The AGA and PP contents required to achieve the optimum damping ratio of the concrete with the least reduction in the mechanical performance were 0.02% and 0.10%, respectively. Furthermore, the addition of AGA was more effective than that of PP in improving the damping property of the concrete.

Influence of the Air-Entraining Agent in the Concrete Coating on the Reinforcement Corrosion Process in Case of Simultaneous Action of Chlorides and Frost

Abstract The paper presents the test results to evaluate the effect of air-entraining agent addition on the intensity of reinforcement corrosion in concrete with blast-furnace slag cement in the case of simultaneous action of chloride corrosion and frost. Two groups of reinforced concrete specimens were prepared for the study. The first group of specimens included air-entraining agent addition and the other group was prepared without air-entraining agent. The blast-furnace slag cement (CEM III/A) was used for the specimens. Two parallel reinforcing rods were placed in each specimen. The specimens were subjected to 120 cycles of freezing and thawing in 3% NaCl solution to induce corrosion on the reinforcement. To determine the occurrence of the reinforcement corrosion and estimate the corrosion activity the non-destructive electrochemical galvanostatic pulse method was used. On each specimen the corrosion current density of the reinforcement was measured as well as the reinforcement stationary potential and the concrete coating resistivity, i.e. values indicating the ongoing reinforcement corrosion. Measurements were made on all specimens in two steps: before freezing and thawing cycles in 3% NaCl solution and after the cycles. The analysis of the obtained results allowed to determine differences in corrosion processes intensity on the reinforced bars in the concrete specimens depending on whether or not the air-entraining agent was added. Based on the analysis it was found that in the case of simultaneous action of chloride corrosion and frost it is advisable to use both blast-furnace slag cement and air-entraining agent. The use of only blast-furnace slag cement (although it is a chloride resistant cement), without the addition of air-entraining agent is insufficient.

Experimental Study on Functional Graded Concrete

The ultimate bearing capacity of thick walled cylinder can be improved significantly by using the concrete functional graded material. The functional graded characteristic of concrete is achieved by the certain variations of the compressive strength and elastic modulus. In order to make use of the functional graded characteristic of concrete, orthogonal experiment are designed in a L16(45) orthogonal array with four factors, namely, “different addition of air-entraining agent (AE)”, “volume fraction of coarse aggregate (VA)”, “maximum size of the coarse aggregate (MS)”, and “water/blinder material ratio (W/B)” and three experimental indexes, namely, compressive strength, elastic modulus and density. The experimental results are analyzed by using the intuitive analysis and analysis of variance (ANOVA). The results show that the addition of air-entraining agent may cause the decrease of the compressive strength, elastic modulus and apparent density of concrete, but it has no significant impacts on the three indexes. The elastic modulus and apparent density are affected significantly by the volume fraction of coarse aggregate and the two indexes increase with the increase of the volume fraction of coarse aggregate. The maximum size of the coarse aggregate has no significant effect on three indexes. The compressive strength, elastic modulus and apparent density of concrete decrease significantly as the water/ blinder ratio increase. The experimental results are used in the model test of thick-walled hollow cylinder. We find that the ultimate bearing capacity of functionally graded two-layered hollow cylinder is greater than that of the conventional thick-walled hollow cylinder.

Assessment and mechanism study of bleeding process in cement paste by 1H low-field NMR

Based on detection technology of 1H low-field nuclear magnetic resonance (NMR), this study developed a novel method for assessment and mechanism study of bleeding. This method is sensitive to bleeding water as well as water in cement paste and diluted grout, gives a vivid scenario of microstructure variation and provides important insights into mechanism of bleeding. In this study, influence of parameters such as cement type, water/cement ratio, chemical additives and environmental temperature on bleeding process was investigated. Results show that bleeding property of cements can be rapidly and precisely evaluated by the proposed method. It is found that peaks of T2 distribution correlate with separated layers of fresh cement paste with bleeding, and the bleeding process generally consists of a significant growth, a relative stable period and a water-sucking stage. Results also demonstrate that retarder significantly increases bleeding, however, bleeding, to a certain extent, can be reduced by the addition of air-entraining agent. Furthermore, bleeding results of the cement paste under different temperatures (15.5 and 22.5°C) suggest that higher temperature leads to a smaller T2 value (around 10ms) and a lower bleeding rate. The high precision of 1H low-field NMR and linear correlation (R⩾0.921) between Rt(B) and bleeding rate both evidenced the superiority and feasibility of the proposed method on study of bleeding.

Experimental Research on New Concrete Air Entraining Agent

Using waste to produce a new type of air entraining agent (AEA), carrying out research of the concrete’s mixture performance, mechanical properties and frost resistance durability after mixing with the AEA, with results showing that amount of air entrained in the concrete mixture and the water reducing rate increases along with the increase of the addition of the new AEA, and its compressive strength loss laws are similar with that of normal AEAs. During the frost-thaw cycle test, when the weight loss rate has reached its limit, concrete with the new AEA added can withstand almost 300 cycles, and at this time the relative dynamic modulus of the concrete, when the amount of air entrained in it is 4.5%, is 83.5%, and the relative dynamic modulus is 85.4% when the amount of air entrained is 5.3%. The addition of the AEA has obviously improved the pore structure of the concrete, and significantly raising its frost resistance durability.