Lime.
Cement.
Proportions.
The mixtures above recommended, 1 to 4 and 1 to 5, will necessarily be somewhat porous, and may be decidedly so if the gravel or screenings used is not properly graded. The water-resisting qualities may be greatly improved, without loss of strength, by replacing a part of the cement by hydrate lime. This is a light, extremely fine material, and a given weight of it goes much further than the {693} same amount of cement in filling the pores of the concrete. It has also the effect of making the wet mixture more plastic and more easily compacted by ramming, and gives the finished blocks a lighter color.
The following mixtures, then, are to be recommended for concrete blocks. By “gravel” is meant a suitable mixture of sand and gravel, or stone screenings, containing grains of all sizes, from fine to 1/2 inch.
1 to 4 Mixtures, by Weight.
- Cement, 150 parts; gravel, 600 parts.
- Cement, 125 parts; hydrated lime, 25 parts; gravel, 600 parts.
- Cement, 100 parts; hydrated lime, 50 parts; gravel, 600 parts.
1 to 5 Mixtures, by Weight.
- Cement, 120 parts; gravel, 600 parts.
- Cement, 100 parts; hydrated lime, 20 parts; gravel, 600 parts.