This paper presents an experimental investigation on the shear behavior of concrete beams of low shear span-to-depth ratios with the high-strength reinforcing steel. Six beam specimens with two different grades of steel (500 and 550 MPa) as the longitudinal reinforcement and three different grades of steel (500, 550, and 600 MPa) as the transverse reinforcement were tested under monotonic loading conditions. Two different concrete grades were considered in the test specimens, whereas the shear span-to-depth (a/d) ratios were varied in the range of 1.05-1.70. The spacing of stirrups in the beam specimens was proportionately varied based on their specified yield strengths for a constant percentage of longitudinal steel. Test results showed that beams with low concrete compressive strength and reinforced with 500 MPa grade longitudinal steel exhibited the diagonal shear failure, whereas the beams with high concrete compressive strength and reinforced with 550 MPa grade longitudinal steel failed in the predominantly flexure mode. In addition to the yielding of longitudinal reinforcement bars, the yielding of stirrups was observed in all beams including the specimen having a higher a/d ratio. It was concluded that the yield strength of transverse steel reinforcement in the concrete beams could be increased to 600 MPa without exceeding the safety and serviceability criteria.
Technological aspects of formation of strength and durability of semi-dry pressed concrete are considered. The main factor that worsens the performance characteristics of products made of semi-dry pressed concrete has been stated. Deformations resulting from the elastic aftereffect phenomenon are manifested in freshly molded concrete at high pressing force. The factors contributing to the reduction of elastic aftereffect deformation have been determined. The complex application of fibers and plasticizer admixture is proposed in order to reduce the destructive processes occurring in semidry pressed concrete in the production of paving slabs. The value of deformations of elastic aftereffect is determined at the pressing intensity of 6, 12, and 24 MPa. An increase of the structural strength of semi-dry pressed concrete up to 320 % was revealed at the age of 4, 6, and 8 hours when reinforced with basalt fibers. An increase of tensile strength at splitting up to 16 % was stated with the combined use of basalt fibers and superplasticizer. The assessment of the durability of semi-dry pressed fiber-reinforced concrete including the water absorption and frost resistance has been performed. Reduction of water absorption of studied concrete with the combined use of basalt fibers and superplasticizer has been stated. A material with a frost resistance grade over F400 has been obtained. The technological line for the production of small-piece products made of fiber-reinforced concrete was developed for the semidry pressing method.
An overview of emerging advances in geopolymer concrete and its mechanical, durability, and microstructural properties are presented. Geopolymer concrete (GPC) is an ecofriendly material used in construction as a good substitute for ordinary Portland cement (OPC) concrete. This concrete has excellent durability properties, better shrinkage behavior, and good resistance to fire attacks. The present review discusses geopolymers formed by the alkaline activation of alumino-silicates and material selection with their properties. Performance of geopolymer concrete made with different pozzolanic materials such as rice husk ash (RHA), fly ash, and ground granulated blast-furnace slag (GGBS) are presented along with the resistance of concrete and mortar to sulphate attack, its acidic nature, and drying shrinkage. Properties of concrete and mortar due to fresh and hardened states are briefly outlined, along with their durability properties. The review on microstructural analysis was also performed to study morphology and elements present in it. Findings reported for geopolymers are compared with ordinary Portland cement to show the effective usage of GPC in construction applications.
