The use of strain relief method is one of the most direct methods for determination of in-place stresses. In this method, a hole is drilled in the concrete member and the change in strain in the vicinity of the hole, on the surface of the member, is measured by means of electrical resistance strain gauges (ERSG). This change in strain due to drilling is used to assess the in-place stress in the member using constitutive relationship and calibration coefficient. This paper presents the experimental application of incremental hole drilling method (IHDM) in concrete under uniaxial stress. A small hole of 25 mm diameter and 40 mm deep was drilled incrementally to estimate the in-place stress in an axially loaded column with minimum damage. Dry drilling was used to eliminate the effect of swelling due to moisture (water) during the drilling. The experimental strain released was then correlated with an analytical solution using the theory of elasticity and finite element method (FEM). The excellent agreement of experimental results with analytical and numerical values of strain released suggests that IHDM can be conveniently used to evaluate in-place stresses in columns.

The objective of this study was to evaluate the effectiveness of colloidal nanosilica (nS) as a nanomaterial and pozzolanic admixture to mitigate the deteriorative effects of sodium sulfate-based physical salt attack (PSA) on portland cement mortars. Mortar mixtures of an ASTM C150 Type II (<8% C3A) or a Type V (<5% C3A) portland cement were prepared with 0, 3, and 6% cement replacements with either nS or microsilica (mS). Test samples were subjected to 3 years of exposure under a constant or cyclic PSA-conducive environment. The PSA results were supported with additional water absorption, rapid sulfate ion permeability (RSPT), and porosimetry testing. The Type V cement mortars containing nS exhibited the most observable scaling and flaking under both conditions of PSA exposure. The addition and increase in cement replacement with nS had a clear detrimental effect to PSA resistance for both cement types and both types of PSA exposure. Results indicated nS reduces permeability and diffusion in mixtures of either cement type which, for PSA, the denser and more refined pore network proved conducive to higher damaging tensile stresses and distress. The larger the measured volume of permeable pore space through absorption, the less susceptible the mortars were to PSA, which is counterproductive to conventional good practice of designing high-durability concrete via reducing permeability and sorption, and increasing a mixture’s watertightness.

Foam concrete is a highly cellularized cementitious material that undergoes extensive plastic deformation when loaded to failure. Under compression, the microstructure of low-density foam concrete gets progressively crushed at a steady stress stage, accompanied by substantial energy dissipation. Understanding foam concrete crushing behavior is of special importance for its engineering applications. However, the current studies are insufficient to define key attributes that are important for material characterization and design. This study focuses on low-density foam concrete ranging from 0.4 to 0.8 g/cm3 (25 to 50 lb/ft3), with the crushing behavior investigated using a penetration test and dynamic Young’s modulus determined using a resonant frequency test. Four distinct crushing phases—linear elastic, transitional, plateau, and final densification—are observed for the samples. Furthermore, the yield strength and plateau strength are identified to characterize the foam crushing behavior. Using the experimental inputs, the modulus-strength constitutive relationship is established for predicting the crushing behavior with fundamental material properties. The findings significantly facilitate subsequent foam concrete studies, as well as the engineering design of this material.

This paper examines the applicability of a recently developed testing protocol to evaluate the potential of sulfide-bearing aggregate—mainly from Ontario—to oxidize and cause damage when used in concrete. The protocol consists of three sequential tests: total sulfur (St), the oxygen consumption test (OCT), and the oxidation mortar bar test (OMBT). The paper suggests modifications to the OCT, and the expansion criteria of OMBT based on testing aggregates with different total sulfur contents. For OCT, using crushing equipment with cast-iron working surface was found to contaminate the samples and give high values of oxygen consumption. The OMBT showed lower expansion values for carbonate aggregates compared to aggregates with silicate. Exposing siliceous aggregate—whether alkali-silica reactive or not—to the high pH and temperature encountered in the OMBT produces high expansion regardless of the oxidizable sulfide content. As such, new expansion criteria are suggested, which take into consideration the silicate nature of some aggregates.

Alkali-silica reaction (ASR) is a major deterioration mechanism that affects the durability of concrete structures. As the slow rate of ASR development and the restrained expansion in field concrete might affect the development of ASR damage, an experimental program was performed to investigate the effects of the rate of ASR expansion and confinement on the degradation of mechanical properties of concretes. Literature data on the degradation of mechanical properties of concretes with ASR expansion were collected and analyzed to investigate the influence of the rate of ASR expansion and confinement on the degradation trends. Degradation of mechanical properties was found to be significantly influenced by the rate of ASR expansion and slightly affected by confinements. The slow rate of ASR expansion seems to be beneficial in limiting concrete degradation. The effects of confinement seem to be related to the direction of restraint and crack orientations.