2. Uniformity of Quality.—In the enumeration of properties needed in a paving brick, uniformity of quality throughout a given lot has been placed second in the list, and it is believed by the writer that it is hardly secondary to the qualities of toughness, hardness, and strength. It is highly desirable that all the brick in a given lot shall be as nearly uni form in make-up as is practicable with the best materials and manufac ture, and especially that brick which will be near each other shall be of uniform quality. If one brick is soft and the next one hard, an uneven surface will be produced more quickly than otherwise, the resulting soft spots receiving harder wear as the low spots appear. A pavement of soft but uniform bricks will wear away at a uniform rate, and its surface may remain less objectionable than one containing a fair proportion of harder brick. The products of some plants are particularly troublesome in this direction, while those of others are fairly uniform. This quality or lack of this quality renders inspection on the street very difficult, and has done as much as any thing to throw discredit on brick pavement. Brick manufacturers will render service to their industry by striving to secure greater uniformity and municipalities must, on their part, protect their interests by holding stricter requirements than in the past. The import ance of uniformity has not generally been sufficiently recognized.
3. Homogeneity of Structure and Freedom from Laminations.— Homogeneity of structure gives uniformity of wear throughout the brick and adds to ability to resist wear and breakage. A brick of homogeneous texture is more likely to possess toughness and strength to the requisite degree than is one of variable texture. Laminations in a brick are par ticularly objectionable, since they markedly decrease toughness and strength, and permit chipping and spalling. It is important that tests for toughness, hardness, and strength be made in such a way as to bring out the effect of laminations and other defects which may not be apparent near the surface of the brick. The brick should be uniform throughout,
evenly vitrified, and free from spots which result from imperfect crush ing and mixing of materials and from any element which will tend to dis rupt the brick by later changes in condition.
4. TVeather-resisting Quality.—Strong, tough, hard brick of low poros ity and even texture are not injured by weather changes. Soft, weak and porous brick are affected by frost and other weather conditions, and a laminated and coarse structure promotes disintegration.
Generally speaking, high grade paving brick are of sufficient strength to withstand weather influences, but the combination of weather effect and traffic is more noticeable. The writer has observed the spalling and grinding of soft brick under heavy loads during the time when they were wet and frozen on pavement where the wear was much slower under better weather conditions. Occasionally a pavement is found where rapid deterioration takes place during the early spring. Part of the trouble of this sort is due to improper bedding and filling.
5. Regularity in Farm and Size.—Well-formed brick of uniform size give a smooth and regular surface to the pavement, and thus add to its attractiveness. Besides, such brick will have uniform bearing and exert even pressure on the sand cushion. below, and thus will remain in position during the life of the pavement. Desirable as this uniformity, is, it does not pay to obtain it at the expense of the wearing qualities, and pavements with the smoothest surfaces do not always give the best results. Some irregularity in shape and form must be expected and permitted, especially with clays of a certain character. No general rule may be formulated, and the amount of irregularity may easily be settled upon in connection with any given lot of brick.