Aggregates are used to give body and strength to a concrete or mortar mix. Coarse aggregate is small stones, usually less that 20 mm in diameter, and fine aggregate is basically sand. Sharp Sand (which has larger grains) is used for concreting or laying paving slabs and Soft Sand is used for bricklaying, etc.Guidelines for Selecting Good Sand that can be used for construction: Silt Content should be less than 3% by weight (12% by volume in 10 min) Sand should be free from Organic materials. Sand shall not contain any harmful impurities such as iron, pyrites, alkalies, salts, coal or other organic impurities.Definition of natural sand. Sand derived from a rock, in which the grains separate along their natural boundaries. This includes unconsolidated sand or a soft sandstone where little pressure is required to separate the individual grains.In making concrete strong, these ingredients should usually be mixed in a ratio of 1:2:3:0.5 to achieve maximum strength. That is 1 part cement, 2 parts sand, 3 parts gravel, and 0.5 part water.What is the difference between cement and concrete Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement.To make concrete though which will greatly extend the volume produced you mix in gravel or sand or crushed brick. Proportions are an endless subject of debate but the formula of 1 part cement, 2 parts sand and 3 parts gravel by volume is a good starting point. Mix the dry ingredients first and then slowly add water.
A mix with little water and more concrete mix will be dryer and less workable but stronger.To make the concrete stronger, add more cement or less sand. The closer you bring the ratio to an even one-to-one of sand to cement, the stronger the rating becomes.However, cracks and damage can occur. Fixing concrete takes a number of materials because it does not readily adhere to other concrete.If you need to patch a concrete surface or pour new concrete on top of old concrete, you must invest in a strong bonding agent and a concrete patching mix.If done properly, new concrete can often be poured right over an existing slab.Hoever, if your concrete is relatively sound and raising its elevation a few inches would not create problems,then you can pour new concrete directly over the old. Well, maybe not directly over the old.The correct mixing ratio would be 1:1.5:1 — 1 cement : 1.5 sand : 1 gravel stones with 0.4 water. If you use more water it will leave holes (porosity of the mortar), and if you use less water, it will not lead to hydration.A concrete mixture ratio of 1 part cement, 3 parts sand, and 3 parts aggregate will produce a concrete mix of approximately 3000 psi. Mixing water with the cement, sand, and stone will form a paste that will bind the materials together until the mix hardens.
Another “old rule of thumb” for mixing concrete is 1 cement : 2 sand : 3 gravel by volume. Mix the dry ingredients and slowly add water until the concrete is workable. This mixture may need to be modified depending on the aggregate used to provide a concrete of the right workability.How to Pour Concrete Over Dirt.Home owners can accomplish the task themselves by pouring the concrete directly on the ground in the installation area. However, the ground must be properly prepared by removing vegetation. In addition, you must construct sturdy barriers to hold the wet concrete in place until it dries.Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting. Gravel is especially important in clay soil because it doesn’t drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains.Though larger pieces of gravel produce more friction and make it harder to mix, they also make a stronger concrete. Water also plays a part in how much sand and gravel to use.Adding aggregate to the mix reduces the amount of water. With less water, the concrete is stronger and less likely to shrink and crack.Add too much water and you’ll ruin the concrete. You can add more Portland cement to bagged concrete to make it stronger. You can also add hydrated lime. To make the strongest concrete, the sand should be sourced from volcanic lava that has a high silica content.