Key Engineering Materials Vols. 629-630

Abstract: In this paper, three bio-mineralization mechanisms were proposed to repair cement-based materials cracks. The common feature is that the three are all induced by bacterial. A type of bacterial which can decompose urea and release carbonate ions could be applied to repair micro cracks on concrete surface when combining calcium ions. But what need to be noted is that the way of repairing cracks is passive. Some alkaliphilic bacterial spores could be added to concrete when casted and two different types of bacterial were used to realize the function of self-healing. The sources of carbonate ions made them different, the one release carbonate dioxide through its own cellular respiration, the other could transfer carbon dioxide in air to bicarbonate. Coefficient of capillary suction, apparent water permeation coefficient and area repairing rate were applied to characterize the repairing effectiveness. The tests results were that all three bio-mineralization mechanisms showed excellent repair effect to small cracks formed at early ages. When the bacteria were immobilized by ceramsite, the self-healing effect could be improved for the cracks formed at late ages.

Abstract: In this study, octyl-triethoxysilane emulsion was prepared using octyl-triethoxysilane monomer. The protective effect of the silane monomer and emulsion was investigated on the concrete with different water to cement ratios (0.4 and 0.5). The results showed that octyl-triethoxysilane emulsion displayed efficient protection of concrete. Octyl-triethoxysilane emulsion acquired excellent penetration depth (> 3.7 mm), the water absorption coefficient was reduced by 83.4%, and the chloride ion diffusion coefficient was only 1.8 × 10⁻¹² m² s⁻¹, reduced by 71.3%. The emulsion also showed good resistance to carbonization and freezing-thawing. The carbonation depth of concrete was reduced by 42%, while the silane monomer has little effect on carbonization. Good protection performance was obtained in the freezing-thawing cycle tests. The relative dynamic elastic modulus was increased by 27%; the mass loss was reduced by 49% after 300 cycles. The protective effect of silane emulsion was also related with the water cement ratio of concrete and the test method. Silane monomer had good waterproof effect and chloride resistance, but poor resistance to carbonization and freezing-thawing. Silane emulsion was a better choice for concrete protection, for it displayed lower rate of volatilization, insignificant toxicity, and better retainment of the active ingredient.

Abstract: Because of the dosage of metakaolin and ash fly had a big impact on the performance optimization of inorganic silicon aluminum polymer, using of metakaolin and ash fly can optimize the pore structure and hydration products of inorganic silicon aluminum polymer paste, how to determine the dosage of metakaolin and ash fly of inorganic silicon aluminum polymer reasonably and directly has become a problem in this research needed to be resolved instantly at hand. The current study investigated the relationship between the amounts of metakaolin and fly ash added and the compressive strength of the inorganic silicon aluminum polymer paste, and then established relevant mathematical model using a quadratic regression quadrature combination design. Previous studies have shown that the addition of 13.56% metakaolin and 3% fly ash would be the optimal plan, and that 57.4 MPa would be the maximum value of the compressive strength of the cement paste of inorganic silicon aluminum polymer that could be obtained. Keywords: Inorganic silicon aluminum polymer; Property Optimization; Quadratic Regression and Orthogonal Design

Abstract: This paper presents an investigation on the mechanical properties of epoxy resin concrete (ERC for short) and its contrast test to cement concrete under the same conditions. It was observed that the strength formation time of ERC is very short and it has higher early strength, the strength formation of ERC has close relationship with temperature. It was found that under the same load, the deformation of ERC is larger than that of cement concrete, namely the toughness of ERC is superior to cement concrete.

Abstract: The coarse aggregate volume fraction in conventional plastic concrete is controlled relatively low to ensure a required workability, but its low aggregate content play negative roll on the service properties of the concrete. In this paper, we revealed the mechanism of a coarse aggregate interlocking concrete prepared by Scattering-Filling Stone Concrete (SFSC), it can keep the fresh concrete its workability but increase its service performance by scattering coarse aggregate during the concrete casting, the experimental and engineering application of SFSC indicated that: the strength of concrete prepared with this method increases obviously whereas the shrinkage decreases significantly when 20% cement dosage is saved. The SFS process was utilized in a highway pavement, the core of the concrete is very dense and no obvious defect could be found when 8% pavement concrete was replaced by coarse aggregate. The SFSC is a type of low carbon concrete.

Abstract: The influence of the content of matekaolin powder and fly ash in cement on controlling ASR was evaluated using Accelerated Mortar Bar Test (AMBT). Replacing cement with matekaolin powder to the extent of 5%,10%,15%,20%,25%,and with fly ash to the extent of 10%,20%,30%,35%,40%, 45% respectively. The result show that matekaolin powder and fly ash both can control Alkali-aggregate activity but to different degrees. Small amount of metakaolin powder exerts significant influence, whereas only when the proportion of fly ash is up to 35%, can it control ASR effectively. The effect and mechanism of the control of the extension of glass aggregate activity was studied by means of SEM analysis.

Abstract: According to current engineering practice, Confined Masonry (CM) buildings are weak in earthquake resistance and difficult in post-quake restoration. A new form of structure, i.e. Hybrid Masonry – Reinforced Concrete Structure (HMRCS), is investigated. By slightly increasing the sizes and reinforcement ratios of the RC members, i.e. beams and columns, which normally only act as confinement in a CM structure, now play an essential role in resisting the gravity load in HMRCS, while the masonry wall mainly resists the lateral earthquake load. To investigate the seismic-resistant behavior, pseudo-static tests on two full-scale HMRCS specimens were conducted, and the measured hysteretic curves were analyzed. Finite Element (FE) simulation was performed to verify the working mechanism and seismic response of the HMRCS specimens. The lateral displacement ductility factor obtained from the experimental results can fully satisfy the seismic requirement of structures. Therefore, HMRCS is reliable if its RC frame members and masonry walls are designed properly. Furthermore, the feasibility of using FE software to study the proposed HMRCS has been validated by comparing the experimental and simulation results.

Abstract: The primary long and short term advantages of high strength concrete are, low creep and shrinkage, higher stiffness, higher elastic modulus, higher tensile strength, higher durability (resistance to chemical attacks) and higher shear resistance. In addition, high strength concrete reduces the size of the member, which in turn reduces the form size, concrete volume, construction time, labor costs and dead load. Reducing the dead load reduces the number and size of the beams, columns and foundations. Thus there is a positive impact on reduction of maintenance and repair costs and an increase in rentable space. Other, yet to be discovered advantages may also exist. High strength concrete has definite advantages over normal strength concrete. The ductility of over reinforced HSC beams is enhanced through the application of helical reinforcement located in the compression region. The pitch of helix is an important parameter controlling the level of strength and ductility enhancement. This paper presents an experimental investigation of the effect of helices on the behavior of over reinforced high strength concrete beams through testing ten helically confined full scale beams. The helix pitches were 25, 50, 75, 100 and 160 mm. Beams’ cross section was 200×300 mm, and with a length of 4 m and a clear span of 3.6 m subjected to four point loading. The main results indicate that helix effectiveness is negligible when the helical pitch is 160 mm (helix diameter). The experimental program in this study proved that the HSC, HSS and helical confinement construct a reinforced concrete beam. This beam has the ability to resist weathering action and chemical attack while maintaining its desired engineering properties. In near future Reinforced High Strength Concrete Beam with Helical Confinement will be considered as a durable and sustainable Reinforced Concrete Beam.

Abstract: In the frame of a research project funded by the Austrian Research Foundation (FFG) a series of 10 UHPC beams with an I-shaped cross-section and a full length of 3.5 m was produced and subjected to four-point bending and shear loading respectively until failure. The amount of longitudinal reinforcement as well as the fiber content was varied. The tensile strength of the longitudinal reinforcement was 800 to 1100 MPa. Several circular shaped openings were foreseen in order to facilitate potential installation crossings. The cross-section was optimized for load bearing capacity and ductility. Special attention was paid on the crack development and SLS criteria as well as the ductility after reaching ultimate load level. The full constitutive law of the applied UHPFRC mixture was derived from compression tests, uniaxial tension tests and several small scale four-point bending tests. On the basis of the derived constitutive law in tension, the UHPFRC was classified as “type 2 – low strain hardening” fiber reinforced concrete.

Abstract: The aim of present work is to further investigate the flexural behavior of FRC with four types of hooked end steel fibers. The flexural toughness of FRC beams was tested under a three point bending system, and the data of experiments were analyzed according to the standard JGJ/T221-2010 and RILEM recommendation. The results showed equal dosage of different aspect ratio fibers didn’t result in the same flexural toughness. It was found that nominal ultimate flexural strength () and equivalent flexural strength () of beams increased as aspect ratio of the steel fiber was increased. However, the highest equivalent flexural strength () was obtained by the fiber with aspect ratio of 67.