"Use fillets on all corners, excepting where the cor ners are built of coign blocks which have been cast separately on the ground and tooled before setting. It is practically impossible to get and maintain a fine arris by moulding concrete in place, and therefore I suggest fillets. Concrete arrises are difficult to cast and main tain; and therefore, on dressed work, I would file the edges to a radius.
"Gravel is practically as good as broken stone for aggregate, but concrete made of gravel cannot be tooled. Small deformations in the mould can therefore not be corrected in spaded gravel work.
"When concrete is to be used as a beam or column, thin wall, or arch, specify the best materials obtainable in your community. Concrete for this class of work must be carefully mixed and placed, to produce a homo geneous mixture.
"On work requiring various grades of concrete, it is more than necessary, in the specifications, to vary the portions of cement, sand, and stone. The quality of the materials might profitably be different, and the method of mixing and placing concrete should be more careful for such work as beams than is necessary in mass work.
"Many engineers seem to think that concrete is con crete, and that the same care should be taken in the proportions, mixing, and placing in one case as in an other. As a matter of fact, you can be a great deal more liberal with a contractor on heavy foundation work than in building a reinforced beam, and the contractor should be given the benefit of this fact.
"In designing, assume that you are going to have unskilled mechanics to do your work. It is almost impos sible to get a good concrete worker unless you educate him, and this is up to the engineer, his foreman, or inspector. This is not the case on other classes of con struction, where the details of construction can frequently be left to experienced mechanics.
"Remember, in designing and also in construction work, that concrete in setting shrinks and that there will always be a very small crack existing between abut ting sections of concrete work executed at different times. Concrete which sets up under a head shrinks less. Concrete rich in cement shrinks more. Concrete made with coarse sand shrinks less than that made with fine sand.
"Detail your bidding sheets so that the bidders can tell exactly the amount and kind of reinforcement re quired. Ask for prices on additional concrete of its several classes, and for additional reinforcement of its several classes. You will find as the work progresses
that there will be many places where extra concrete and extra reinforcement arc desirable.
"Specifications. Don't finally pass upon specifications until your drawings have been finished and approved. Be careful to specify material which can be procured, and preferably what is commonly in the market. This will save your client money, and yourself considerable bother.
"Don't specify methods of procedure on work in which you are not experienced. You can get experienced bidders competent to lay out their own method of pro cedure; and if not, a closer study of the subject than is frequently possible in the writing of specifications will enable you later to determine upon better methods than can be decided upon off-hand.
"Remember that no specifications at all is better than bad ones. Just say that the work shall be first class according to the common practice in your own vicinity (or some other, if it is better), which is about all that is intended by most specifications. If you take upon yourself the authority to specify in detail just exactly how a contractor is to proceed with the work, do not then specify that the contractor shall be respon sible for the work. If you want the contractor to be responsible for the work, write a general specification describing the class and character of work desired, leaving the details to the successful bidder to work out.
"Don't put things in the specifications which you do not mean to enforce, as it costs your client money and frequently keeps away desirable bidders. Sometimes engineers put in club clauses for the purpose of keeping contractors in line. This is, of course, unnecessary.
"Don't copy old specifications blindly. You can seldom use a standard specification for concrete without adapting it to local conditions. Don't preserve dead letters in your specification. Here are a few clauses which I incorporated in my own specifications in 1898, but which have been omitted in more recent ones; I think they will still be found in use by a great many engineers in their specifications, but not in the actual construction : " 'Concrete shall not be passed down to its place through a chute or thrown or dumped from a height, but must be carefully lowered in a vessel, and so carefully placed as to contain the constituents evenly incorporated as mixed and entirely free from foreign matter of any kind.