Mechanical Properties of Low-Performance Concrete (LPC) and Shear Capacity of Old Unreinforced LPC Squat Walls.

Low-performance concrete (LPC) is characterized by its low strength and commonly by the presence of large aggregates. This type of concrete was used for construction of load carrying, commonly unreinforced walls in old buildings. The resistance of these buildings with LPC squat walls (of relatively low height-to-length ratio), to in plane horizontal loads, was experimentally investigated in this study. The low compressive strength of these walls, well below that of standard concrete, requires estimation of the relation between the actual LPC compressive strength and its tensile strength, and identification of their failure mode and corresponding shear capacity when subjected to in plane horizontal loads. In this study, compressive and splitting tensile strengths of authentic LPC specimens were measured, and based on them, a relation between the compressive and tensile strengths is proposed. Then, diagonal compression tests were performed on authentic LPC specimens, as well as specimens made of standard concrete. These tests yielded the expected mode of failure of vertical cracking and their analysis shows that their shear capacity needs to be evaluated based on their tensile strength (rather than the flexural shear capacity of unreinforced concrete beams). Thus, the load-bearing (both horizontal and gravitational) capacity to prevent diagonal tension failure of an unreinforced LPC wall can be evaluated by comparing the LPC tensile strength to the major principal stress caused by the load. Assessment of the tensile strength can be based on the relation between the compressive and tensile strengths proposed in this work.

High-performance concrete engineered for protective barriers.

This paper reviews the effects of high-performance concrete mix ingredients on its resistance to impact of non-deforming projectiles, and on the resistance of layered barriers, engineered based on these findings. First, the reported effects of the aggregate types and sizes and the application of steel fibres, which were observed experimentally, are presented, considering resistance parameters that include the impact energy at the ballistic limit, the extent of the damaged areas at the impacted (front) and rear faces and the overall damage. These findings indicate that a protective barrier may be engineered to have layers that utilize these effects to produce a better performance under impact. Results from reported experiments of double-layered specimens, which examined the effects of the aggregate size and application of fibres, confirm this idea to a certain extent. They lead to conclusions regarding the importance of fibres in mitigating the damage, the use of large aggregates in a thicker front layer and their associated effect on increasing the damage at the front, impacted face. A 'resistance index' is proposed to quantify the resistance in a comprehensive way and the experimental results have been re-evaluated in view of this parameter.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.