CORRESPONDENCE.

Timaru Herald, Volume LXII, Issue 2887, 12 December 1898, Page 3

CORRESPONDENCE.

♦ THE BREAKWATER. TO THE EDITOR OF THE TIMARU HERALD. Sir,— Some of Mr Marchant's opinions as expressed by your representative are correct enough, but to others very great exception can be taken. He says good concrete cannot be made from shingle. In this 1, and engineers other than Mr Merchant, "iffer from him. If any one will take the trouble to examine, they will find that most of the rubble put into concrete is quite loose, while the shingle is welt cemented together. This of itself shows that there is some other reason, besides the smoothness of theshingle, why the concrete is not good. Again, the foundation blocks where they project above the water are perfectly sound and so are those placed at the entrance end of the breakwater (not random blocks) there is no sign of chemical action there. Also the eariy part of the breakwater built by Mr G. Stumbles is perfectly sound and hard as when first built, and that is the reason why I think they'have dove a wise thing m making him foreman over the repairs. These facts go to show that there must be some other reason beside smooth shingle and quantity of cement causing the faulty work. I will try to explain what, mmy opinion, i 8 the real reason. You will remember that when a piece of disintegrated concrete was sent for analysis, the gist of the report was that the concrete was porous, allowing the air and water to enter. This is the sole reason of the failure of the breakwater, from the curve outwards. In my opinion the reason why this part of the breakwater is worse than the other is that it is further away from the mixing plant. The concrete was carried m boxes holding about 14tons. Now, it takes a consideraable time to mix that quantity of concrete, and it took a considerable time to take it to its destination, nowhere less than half a mile, and by the time it got there it was partly set. Anyone who saw it emptied from the boxes will remember that there was some difficulty m getting it out. Now, concrete m this state cannot pack solid especially when it is filled with lumps of rubble. This, I think, is quite a sufficient reason why the concrete m the outer kantof the breakwater is a failure. If it is desired to make it solid it ought to be mixed on the spot, and there is no reason why it should not be. It could be just as easily mixed there as anywhere else. The main conditions required m making good concrete are. that there must be sufficient mortar, that is cement and sand, to fill up completely the spaces between the shingle or rubble, and that it must be fluid enough to make it flow and pack solid without ramming. Mr Marchant is quite right about the blocks which fell to pieces on the parapet. They were made before his time. Covering the outside of the breakwater with rubble would protect it of course, but I think there are two other ways of doing it. One is by taking the shingle away, and the other is allowing or causing the shingle to bank up against it and forming the protection itself. Then there wouid be only a small piece at the end which would be exposed, and that would be m such a direction that the shingle would have little effect on it. You must remember that the rubble would want keeping up, but the shingle, would repair itself. I am, etc., War. Parr.