U-value describes how much heat moves through a building element for each degree of temperature difference. It’s literally the rate of heat transfer per unit area, with units of W/m^2K. That means a higher U-value indicates more heat slipping through, and a lower one indicates better insulation. The U-value is the reciprocal of thermal resistance (R-value), so increasing resistance lowers the U-value. It’s not a measure of the material’s thermal conductivity alone (that’s a property k of the material) and it’s not about sound insulation.

The main idea is that ASR relies on a reactive silica in aggregates reacting with alkalis in the cement pore solution to form an expanding gel. If the aggregates are non-reactive, they don’t provide the silica that would participate in that reaction, so the gel can’t form (or forms far less), and the expansive pressure that drives cracking is reduced. In other words, non-reactive aggregates act as inert fillers with respect to ASR, lowering the risk of expansion and damage. This isn’t about curing temperature or speeding up the reaction—those would not be the mechanism here—and there is a real reduction in ASR risk when reactive silica is avoided.

Alkali-silica reaction expands concrete when moisture allows alkalis from cement to attack reactive silica in aggregates. A proven way to curb this is to add supplementary cementitious materials that react with the alkaline pore solution, reducing its availability and slowing the reaction. Fly ash is a pozzolanic material; its reactive silica and alumina react with calcium hydroxide from cement hydration to form additional cementitious products. This consumes the caustic components, refines the pore structure, and lowers diffusion of alkalis to the reactive silica, so the ASR gel forms less and swells less. Because of this mechanism, fly ash is commonly used to mitigate ASR. Other options don’t provide the same reliable pozzolanic activity: limestone mostly acts as filler, granite is inert, and bentonite’s effects are less consistent for ASR control.

Seismic retrofit strategies are aimed at improving how structural materials perform when the ground shakes, specifically by increasing both lateral strength and ductility. Strength helps the structure resist the horizontal forces generated during an earthquake, while ductility lets it deform significantly without suddenly losing load-carrying capacity. This combination allows the building to absorb and dissipate energy, reducing the risk of catastrophic collapse and keeping occupants safer. Options that focus on material costs, fire resistance alone, or reducing stiffness don’t address the essential dynamic performance needed during seismic events. Retrofit methods like reinforcing joints, adding shear elements, or wrapping vulnerable members directly enhance these material properties to better withstand earthquake demands.

Moisture resistance in a substrate is crucial for wet areas because the material must not absorb water, swell, or promote mold and deterioration when exposed to humidity or direct splashes. Cement board fits this need best among common options because it is a cementitious, dense substrate that resists water infiltration and provides a stable base for tile and thinset. It doesn’t swell or warp like some wood products and doesn’t crumble like gypsum-based boards when exposed to moisture, making it ideal for showers, tub surrounds, and other damp environments. Plywood can handle some moisture better than gypsum products, but it can still rot, delaminate, or warp with prolonged water exposure if not properly sealed and maintained, so it’s not the standard choice for wet zones. Gypsum wallboard and regular drywall have gypsum cores that readily absorb moisture, leading to swelling, mold growth, and deterioration in wet conditions, which makes them unsuitable for wet areas.