ALL CONSTRUCTION CLOSELY ESTIMATED

All Construction Closely Estimated By Department

By J. S. MILLS, Engineer of Estimates Throughout all the various stages of preparation and construction, from the time the plans leave the drafting room as completed until the final quantities due the contractor are checked, this Division handles the detailed papers necessary to the construction of the project. This might seem rather extraordinary, but it can be seen readily that the various stages are closely related and, in fact, interlocking. For instance, the first step taken in initiating a project for construction is the preparation of the P. S. & E. (Plans, Specifications and Estimate) for submission to the Bureau of Public Roads, and it is necessary at this time for us to investigate in detail methods, means, materials, and manipulation. Although we never go out "on location," as they say in Hollywood, to see the particular road on which we are asked to figure the cost, we get a pretty fair idea of what the contractor will have to contend with from field reports and conversations with the various District Engineers. Having these data at the first inception of the work, we can prepare intelligently the detailed specifications and estimate, and it is logical and practical that we "carry on" to the final completion of construction.

Again, in the preparation of the detailed estimate, there is a certain amount of routine work which is necessary and which must be done in detail and for which we prepare various charts, diagrams and tables. Our Resident Engineers, who are alert for any shortening of their paper work, have requested copies of these papers for use in the field. The use of these charts, diagrams and tables which cover methods, means, materials and manipulation from beginning to end, besides standardizing the work, dovetails the field work to our own and effects a real saving in time and labor, and also has had the effect of increasing the accuracy of the returns.

When it is known that the average job takes about six months to construct, which means six monthly estimates and the final check, and that the number of reports and papers handled each month from a job averages about thirty, and there are close to fifty jobs going on at the same time, this standardization really amounts to something.

To further correlate and simplify the work, we issued a Manual of Instructions to Resident Engineers of a size readily carried in the pocket. This Man-

Sand Is Important Factor In Concrete Construction

By J. W. POWERS

Engineer of Materials

The everyday usage of this term covers many and various gradings from the fine beach sands to the coarser felspar crystals of disintegrating granite. Somewhere in between is the ideal for use in concrete. Primarily upon sand depends the workability of concrete. The correctness of this statement might be questioned but it is essentially true.

All rock eventually disintegrates and it is this disintegration which produces sand. However, all rock disintegration does not produce a satisfactory sand and even though the resulting sand has come from a satisfactory rock, there are other agencies which affect its value for construction purposes.

1-STRENGTH-The strength of a sand is determined by comparing a 1-3 mix by weight with 1-3 mix by weight of Ottawa sand (standard sand). A 1-3 mix is one part cement to three parts sand. Both compression and tension comparisons are made. In each case the sand to be acceptable must have a mortar strength equal to, or more than, the standard.

2. GRADING-Upon the grading of the sand depends its usefulness and, to some extent, its results in tests. If it is too fine it will not pass the strength test, and if it is too coarse, workable concreteual covers thoroughly all of the required forms checked by this Division, and gives detailed instructions on how to properly cannot be made with it. Our specifications at the present time require not more than 5 per cent retained on onequarter (4") inch screen, not less than 25 per cent nor more than 50 per cent passing 30 mesh, and not over 5 per cent passing 100 mesh. Of the many gradings within this specification those that approach the upper limits place the most easily and give the best finish to concrete.

3. COLORIMETRIC-This determination is to detect the presence of organic matter. The presence of organic matter in sand is determined by allowing it to stand for 24 hours in a 3 per cent solution of sodium hydroxide. Its presence is shown by color imparted to the solution above the sand. Organic acids attack the bond of cement thus giving a lowered strength.

4. SILT-While this item might be dealt with under grading, it really does not belong there due to the fact that no grading analysis is made of it other than we know it will all pass a 100 mesh sieve. The maximum limits on siit are 3 per cent. The silt determination is made by washing the sand and pouring off the silt that remains in the washing water. The exact procedure is to wash fifteen seconds, allow to stand fifteen seconds and then pour off the liquid above the sand. This process is carried on until the water poured off is clear. Silt in well graded sands is a detriment in that it will give lower strength than one practically silt free, but in coarse sand it acts similar to an admixture in that it promotes workability without lowering the strength.

Fill them out, together with various tables and charts to simplify the computation of the different items, such as concrete, steel, excavation, etc.

One of our interesting duties is the distribution of standard specifications. These have been distributed to nearly every state in the union on an exchange basis on which, for a copy of our specifications, we secure a copy of their specifications. Foreign countries are not on this exchange basis. We do, however, distribute a number of standard specifications on requests from the different foreign countries, but never ask that they return us a copy of theirs, for reasons which are well-another story. The United States of Soviet Russia seem to be very much interested in Arizona's specifications, as we have had several requests from that country. Luckily these letters were written in English, therefore, we are neither cross-eyed nor troubled with laryngitis.

Even the best headlights will get out of adjustment when subjected to hard driving. As a result their beams will be so directed that they are blinding to other drivers and they will also fail to light the road properly. Headlights should be given periodic inspection. If the motorist tests them or has them tested once a month, he may be reasonable certain that his lights are in proper condition.

Although nearly three million automobiles were consigned to the junk heap last year, there remain in service more than three million that were produced seven years ago or earlier. Dealers are being encouraged to junk as many old cars as possible. An estimate of 7.23 years is given as the average life of a car and when normally it is ready for the junk heap.