Surface cracks have appeared on concrete that was recently placed. Are these likely to enlarge and cause the concrete to spall or crumble?
Although crazing is unsightly, early crazing does not ordinarily indicate the beginning of deterioration. It can appear at any time up to several weeks after placing. Crazing is caused by some combination of circumstances that causes the surface to shrink slightly faster than the body of the concrete. For example, it may occur when concrete has been placed on a dry, hot, windy day, or even during cool, damp weather if the concrete temperature is higher than that of the air. It can also develop from temperature stresses introduced by the use of cool curing water on a hot concrete surface. Finishing that is too early, while bleed water is still present, is likely to produce a surface that is weak and more susceptible to crazing than otherwise. Sprinkling water onto concrete that is too dry for proper finishing may do the same thing. If dry cement is sprinkled over a surface that is too wet to trowel, as a means of speeding up the operations, it may cause crazing by drawing water rapidly from the surroundings. Crazing can be prevented by organizing the work properly to avoid delays that could allow the concrete to stiffen too soon, by using the right amount of finishing at the right time, and by protecting the surface from excessive rates of drying during finishing. Sun shades and windbreaks are useful. Unless humidity is unusually high it is also helpful to cover concrete with polyethylene after each finishing operation until time for the next operation to start.