The crack has had water applied prior to having cleaner applied. A wire brush is then used to ensure the cleaner is distributed through-out the crack surface. Note the white, frothy appearance. This is usually a sign that the current application of the cleaner is effective. If there is heavy soil or other accumulation, the cleaner will quickly become brown and there will be very little suds or frothing. This is usually an indication that another application will be required following a rinse and wet vacuuming.