PRESERVATION OF CONCRETE

Southland Times, Issue 23840, 10 June 1939, Page 21

PRESERVATION OF CONCRETE

IMPORTANCE OF RETAINING WATER CONTENT The importance of retaining the water in concrete, and the methods for ensuring its retention were discussed by Mr J. B. Rowntree in a paper presented to the last meeting of the Southland branch of the New Zealand Institution of Civil Engineers. Mr Rowntree said that the cement in concrete might to some extent be regarded as the glue which held the mass together. The more water that was added, the weaker became the cement solution, with the result that poorer concrete was obtained. Whereas glue became set by the drying out due to the loss of water, a good deal of the water in concrete was required by the cement, and for satisfactory results none of the water which had once been mixed with the cement, whatever the quantity, should afterwards be lost. As it took some time before the chemical action of the setting of the cement was far enough advanced even to seal off the mass partially, it followed that unless precautions were taken the water was free to evaporate. Actually it did so very readily. The space occupied by the water was then left as minute voids, as nothing except air was left to take its place. This prevented the full strength of the concrete being obtained, and, more important, channels were left which allowed the flow of water through the concrete. These also provided points of attack by frost and atmospheric acids, greatly reducing the durability of the structure.

1 The speaker conculded by mentioning the results of experiments with various methods of treatment, including “ponding” the surface with water, covering with waterproof paper, earth, sand, or straw and spraying with bitumen or tung oil mixtures.