Rich and Poor Limes may be mixed with a large proportion of sand (3 or 4 measures of sand to 1 of lime), for in any case they make mortars with very little strength. Hydraulic Limes make a good mortar with 2 of sand to 1 of lime. Roman Cement Mortar should not have more than 1 or 1½ sand to 1 cement, and is then a very weak mortar. Portland Cement will make a very strong mortar when mixed with 2 or 3 of sand, and even with 5 of sand - a mortar better than any of those made from lime.
Concrete is a conglomerate or thorough mixture of shingle, broken stones, or similar material, with lime or cement, sand and water, which form a mortar filling the interstices between the pieces of stone. The proportions of ingredients mixed determine the quality of this mortar, which in its turn governs the strength of the concrete.
Concrete is generally described with reference to the bulk (when dry) of the materials comprising it. Thus for an important work the concrete might be 1 Portland cement, 2 sand, and 5 of shingle or broken stone ; for less important work 1 Portland cement, 3 sand, and 8 shingle.