Extensive cracking in thousands of residential concrete foundations in eastern Connecticut is found to be due to two-stage expansions associated with oxidation of pyrrhotite in crushed gneiss coarse aggregate of concrete used from a local quarry that sits on a hydrothermal vein of significant pyrrhotite crystallization, followed by internal sulfate attack in concrete from the sulfates released by pyrrhotite oxidation. Microstructural, chemical, and mineralogical evidences of pyrrhotite oxidation and the resultant internal sulfate attack in concrete are presented from a case study. A five-step laboratory testing protocol is suggested for assessment of aggregates from the area to prevent pyrrhotite-related deterioration for future construction.

The construction of foundation and basement walls in residential and small building construction often involves the use of low-quality con-crete. Such concrete can exhibit excess cracking and low impermeabil-ity, hence affecting the quality of habitation. This paper reports the results of a field-oriented study carried out to demonstrate the suit-ability of high-performance, self-consolidating concrete for the con-struction of basement and foundation walls. Two optimized mixtures were first used to cast 4 m 3 L-shaped experimental walls measuring 15 x 1.2 x 0.2 m. The easy-flowing yet cohesive concrete was shown to spread through the narrow unrein-forced formwork and fill it in. The mean spacing factor and rapid chloride ion permeability were determined along the walls and were shown to vary between 120 and 175 µm and 575 and 900 coulomb at 56 days, respectively. The mean compressive strength of such con-crete ranged between 8 and 16 MPa after 1 day, and 50 to 60 MPa after 56 days The in-place compressive strength after 56 days varied between 30 and 40 MPa for the self-consolidating concrete made with 20% fly ash and 3% silica fume replacements (w/cm of 0.45), and 42 and 50 MPa for the richer mixture with 40% slag and 3% silica fume replacements (w/cm of 0.42). The strength decreased slightly near the top of the walls and away from the casting position. The silica fume slag concrete was used in the casting of the perimeter foundation walls of a three-townhouse complex at the Canadian Centre for Housing Technology in Ottawa. A total of 36 m 3 of self-consolidating concrete was used to fill the basement walls measuring 12 x 18 m in plan, approximately 2.5 m in height, and 0.2 m in thickness. The concrete was cast from opposite corners and was shown to spread readily into place and self-level, resulting in a high-quality surface finish.

The first signs of global warming caused by the greenhouse effect are now apparent. In the near future, a new evaluation of building materials in light of their ability to fulfill the requirements of sustainable development will be required. In this paper, the energy consumption and greenhouse gas emissions of concrete in residential buildings will be examined, taking into consideration production and operational phases, as well as traffic-induced energy consumption and emissions in residential areas. The massiveness of concrete buildings causes significant energy and emission savings compared to buildings comprised of lighter materials. This improves the ecological balance of concrete and lifts it to the group of building materials which burden environment least.