International Concrete Abstracts Portal

This research examines the hole-drilling method per ASTM E837, known for its minimal invasiveness, for measuring in situ stress in reinforcing bars embedded within concrete structures. The primary objective is to ascertain the applicability of this method in estimating non-apparent stresses, such as those resulting from the external loads, creep, shrinkage, or alkali-silica reaction, that are needed for structural assessment. Systematic experiments on reinforced concrete beams are conducted to validate the method’s viability in identifying these critical in situ stresses. The findings highlight the potential of the hole-drilling method to enhance structural health monitoring practices, offering an accurate tool for assessing stress states crucial for the maintenance and safety of concrete structures. The results demonstrated that while the hole-drilling method is robust for moderate-stress evaluations (up to about 70% of the nominal yield stress), it overestimates the stress in the reinforcing bar under high-stress conditions near the 100% nominal yield stress. This study contributes to the field by confirming the limits and applicability of the ASTM E837 standard for estimating the existing stress in the embedded reinforcing bars.

According to Section 5.4.3 of ACI 370R-14, when design of concrete structures involves containment of internal explosion effects, both shock waves and gas pressures should be considered. For high explosives (HE) detonations, empirical relationships for predicting gas loads are provided in UFC 3-340-02. Logically, the TNT (Trinitrotoluene) equivalencies for low explosives (LE) such as propellants and pyrotechnics are used in some cases to predict the internal gas pressure-time histories, as mentioned in Section 5.2.2 of ACI 370R-14. Section 5.2.2 also points out that “the designer should insist on an adequate determination of TNT equivalency, including energy, pressure, and impulse equivalents.” However, the confined burns of LE without venting generates deflagration so that the gas pressures can last tens of minutes or even hours as long as the internal temperature decays are slow enough. Thus, any dynamic analysis such as single degree-of-freedom (SDOF) is not applicable herein. The confined burns of LE with venting involve complex convective combustion processes where chemical/combustion and aerodynamic experts should play an important role in predicting gas loads. As a result, this paper provides the evidences on why the TNT equivalency should not be used in blast design for containment of confined burns of LE. This paper also provides the simplified procedures in estimating the quasi-static gas loads for the confined burns of LE without and with venting, after briefly comparing intrinsic characteristics in HE detonations with those in LE burns.

On May 23, 2024, representatives from state agencies, researchers, designers, contractors, and startups gathered for the NEU Spring 2024 Summit. The summit focused on learning about the challenges and barriers impeding the implementation of low-carbon materials as well as how NEU: An ACI Center of Excellence for Carbon Neutral Concrete might aid in overcoming those challenges.

Designed to look like a stacked flowerpot, the cast-in-place concrete IQON apartment building is the tallest building in Quito and the third tallest in Ecuador. Concrete construction made it possible to create a structure with greenery on its façade. Apartments feature terraces with planters containing one or more trees and plants like those found in adjacent La Carolina Park.

A large volume of freshly produced and harvested coal ash (from landfills and ponds) contains SO₃ content above 5.0%. This exceeds the allowable limit in major SCM specifications (e.g., in ASTM C618), and disallows the use of such coal ashes in concrete. This presentation explores the properties and performance of these coal ashes as SCM. It is shown that SO₃ may be present in ash in the form of CaSO₃, CaSO₄, or Na₂SO₄ (including solid solutions of alkali sulfates and carbonates), and that the form of SO₃ has a large impact on the performance of coal ash in concrete. For example, while ashes containing CaSO₃ may cause extensive set retardation, those containing CaSO₄ may increase the risk of internal sulfate attack and deleterious expansion. In this work, the mechanisms responsible for each behavior are explored, the allowable SO₃ limits are better defined, and strategies for beneficiation of coal ashes that exceed such limits are introduced. The outcome is facilitating the safe and efficient use of large volumes of currently off-spec coal ash to produce durable and low-CO₂ concrete.