QUALITIES OF HIGH GRADE PAVING BRICK AND TESTS USED IN DETERMINING THEM.
The extensive use of brick for street paving purposes makes the formulation of the qualities requisite for a good paving brick a matter of importance to both producer and consumer. Although it may not be difficult to agree on these qualities in the abstract, it is not easy to ex press the requirements in definite and concrete form and in terms accept able to both manufacturer and municipality. It is an accepted principle that the quality of an engineering material should not be left merely to the judgment of an individual, no matter how experienced the individual may be; recourse should be had to physical tests and these should be definite and discriminating. Such tests may not of themselves be con clusive, the results are in the nature of evidence which must be inter preted and judged in the light of other information. Perfect materials for a pavement may not be obtained and high quality usually means increased cost of production, but on the other hand the additional cost of a good article is usually made up many times over in the increased length of life and improved surface of the pavement as compared with a pavement in which an inferior brick is used. The problem of formu lating requirements and making tests is further complicated by the diffi culties encountered in selecting brick for test and comparison from the piles of brick along the street and in judging whether the variation from the average throughout these piles is sufficient of itself to be cause for re jection. Enough has been said to justify the view that the formulation' of the qualities needed in a high grade paving brick and the use and interpretation of physical tests for determining the qualities of the brick for aiding in deciding whether brick come up to the required grade, are matters worthy of discussion by engineers and manufacturers. A general statement of matters connected with brick testing may be of advantage to many who are interested in the construction and use of brick pavement.
Most specifications for materials set forth qualities of materials to be furnished by the producer to the consumer. In the case of brick pave ments the producer (i. e., the manufacturer) and the consumer (i. e., the municipality and the property owner, as represented by the municipal administrative officers) are to use certain requirements to define the ma terial to be put into the pavement. Some of the purposes of these re quirements and tests may be expressed as follows : 1. To make a basis or definition of what is wanted and what is to be furnished. This is the commonly accepted purpose of such requirements and tests.
2. To enable the city to secure material which will be as serviceable as other material which has passed the requirements and which has stood the test of traffic and time. This makes the tests in a sense a guaranty of quality.
3. To enable comparisons to be made between the products offered. It is quite possible that tests may show that a given brick is above the require ments, or that a slight difference in price is made up many times by the superior quality of the article.
4. To improve the general quality of the product put on the market. It has frequently happened that the formulation of requirements and the care ful inspection of the articles offered have resulted in improved quality and this in many cases even without increasing the cost of production. The manufacturer has been stimulated thereby to study the process of production and to seek to improve methods of manufacture and quality of product. One need instance only structural steel and paints and oils to show improve ments in quality following carefully made requirements and tests to show the beneficial influence of adequate inspection and tests.
5. To safeguard the interests of the public and of the taxpayer. The Ilfl nois law requires, and rightfully, too, that the nature and quality of the improvement shall be explicitly stated, and evidently intends that the tax payer may be able to determine (1) what the improvement is to be, and (2) whether it is being put in as described.
6. In the occasional cases where abuse of authority or improper or dis honest construction may require a check, to enable control to be exercised over incapable or dishonest contractors or city officials, and to restrain care less or inefficient employes, or men who may have a mistaken notion of what their employer's interests are.
7. To educate producer, consumer, and their agents in a knowledge of the qualities needed in paving brick,—from the manufacturer and the .contractor and their employes to the mayor, the engineer, the inspector, and the prop erty owner. It should be recognized that those who have charge of munici pal work are a constantly changing class, and that the property owner may have little knowledge of pavement construction.
S. Not the least important of the reasons for having an explicit and definite statement of the qualities and requirements for a paving brick is to give the opportunity for all bids to be made on the same basis and for the bidder to fix his price according to the quality of the article wanted and thus to facilitate fair competition.
It is evident that a knowledge of the qualities of a high-grade pav ing brick and of the defects to be avoided in the selection of brick will be useful in making up the requirements defining the grade of brick to be used and that the method of making tests ought to be studied both in relation to the wear of the brick in the street and to the bearing of the results of the physical tests upon the wearing and other qualities of the brick. In this article a discussion of the qualities needed in a paving brick will be given first, and the bearing of the tests upon these qualities will then be taken up, though it will be seen that the relation between the method of testing and the quality to be determined is so intimate that their discussion must be carried on together to a considerable extent.