To know the best concrete sand ratio, we should know the concrete sand ratio calculation formula, and the effect it has. This article will introduce how to determine the best concrete sand ratio and some knowledge about concrete sand ratio.

Here is the outline.

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## The concrete sand ratio calculation formula

SR=S/(S+G)*100%

SR = Sand ratio

S = Amount of sand

G = Amount of gravel

Changes in sand ratio can cause significant changes in the total surface area of the aggregate, which has a significant impact on the consistency of the concrete mix.

The principle of determining the sand ratio is that the best sand ratio to ensure the cohesiveness and fluidity of the concrete mix, under the premise that the cement paste is the most time-efficient. The effect of the sand ratio on the consistency is very significant.

## Effect of concrete sand ratio

### The effect of concrete sand ratio on fluidity

Under the condition that the amount of cement and the water-cement ratio is certain, as the mortar composed of sand and cement slurry plays the role of lubrication and roller bead between coarse aggregates, it can reduce the friction between coarse aggregates. So in a certain range, as the sand ratio increases, the fluidity of concrete increases.

On the other hand, due to the total surface area of sand is bigger than the coarse aggregate, as the sand ratio increases, the total surface area of coarse and fine aggregate increases, under the condition that the amount of cement slurry is certain, the amount of slurry wrapped around the surface of the aggregate thins, and the lubricating effect decreases so that the concrete fluidity decreases. So if the sand ratio exceeds a certain range, the fluidity decreases with the increase of sand ratio.

### The effect of concrete sand ratio on cohesiveness and water retention

As the concrete sand ratio decreases, the cohesiveness and water retention of concrete decrease. It is easy to produce water secretion, segregation, and flow phenomenon. As the sand ratio increases, the cohesiveness and water retention increase. However, when the cement slurry is not enough to wrap the surface of the aggregate, as the sand ratio is too large, the cohesiveness decreases.

## Determination of the best concrete sand ratio

The best concrete sand ratio means that the sand fills the gravel voids and has a certain amount of surplus, which can form a certain thickness of mortar layer between the gravel, in order to reduce the frictional resistance between the coarse aggregates, so that the concrete fluidity reaches the maximum. Or in the case of maintaining the same fluidity, make the minimum amount of cement paste. Adjustment of consistency – to determine the base ratio.

According to the preliminary calculation of the ratio of the concrete mix, first determine the concrete slump, while observing the cohesiveness and water retention. If it does not meet the requirements, make adjustments according to the following principles.

(1) When the slump is below the design requirements, increase the amount of water and the corresponding amount of cement (cement slurry) while keeping the water-cement ratio unchanged.

(2) When the slump is above the design requirements, increase the amount of sand and gravel (equivalent to reducing the amount of cement slurry) while keeping the sand ratio unchanged.

(3) When the cohesiveness and water retention are poor (usually insufficient sand ratio), the amount of sand can be increased appropriately, that is, to increase the sand ratio.

(4) When the mix appears to be too much mortar, you can add the right amount of gravel alone, that is, to reduce the sand ratio. The sand ratio is one of the main factors affecting the workability, apparent density, strength, and deformation properties of high-strength light-aggregate concrete.

The use of the best sand ratio can not only increase the strength of light aggregate concrete but also improve the fluidity of light aggregate concrete. The strength of high-strength light-aggregate concrete fluctuates with the increase of sand ratio and reaches the maximum strength when the sand ratio is 42%. This is mainly due to the fact that the voids between coarse aggregates are not filled densely when the sand rate is below 42%. As the sand ratio increases, the void ratio decreases. The concrete is more dense, so that the strength is improved.

After the sand ratio is higher than 42%, as the sand ratio increases, the number of coarse aggregate decreases and the number of fine aggregate increases, while the amount of cement remains unchanged so that the degree of compactness of the mortar itself decreases, and the interfacial reinforcement and mechanical engagement between the ceramic particles and the cement stone decreases. When the concrete is damaged, the strength of light aggregate concrete is reduced along the two forms of damage of the ceramic particles themselves and interfacial damage at the same time. And the too-high sand ratio is easy to produce delamination and segregation and water secretion, resulting in reduced stability of light aggregate concrete, the strength is reduced instead.

Therefore, when formulating high-strength light-aggregate concrete, attention should be paid to the selection of the best sand ratio in order to achieve the most optimal.

## How to adjust the concrete sand ratio?

We need to measure the water content and gravel content of sand, and then adjust it according to the ratio.

1. CS=RS/(1-SG)(1-SW)

CS = Current sand

RS = Ratio sand

SG = Sand with gravel

SW = Sand with water

For example:

sand containing 3.5% water, containing 20% gravel, ratio sand 856.

CS= 856 / (1-0.2)(1-0.035)= 856 / 0.772 = 1109

From the above we know the amount of sand now, the sand contains gravel is around 221, it is to constantly adjust constantly according to the sand and gravel on site. The water content and gravel content of each batch of sand should be constantly measured to adjust the ratio.

2. Do the sand sieve analysis to see how the sand gradation

According to each sieve residue to see how many zones of sand. If the sand is in one zone, the sand ratio should be increased, in order to have enough cement to meet the concrete’s consistency; if the sand is in two zones, the sand ratio should be reduced appropriately.

3. Cement content of sand

The requirements for frost resistance and seepage resistance are more stringent. Containing less cement is better for the consistency of concrete. High cement content has an impact on strength. The water requirement is large, invariably the water-cement ratio is large.

Also to read:

Slow-setting Problems of Ready-mixed Concrete & the Preventive Measures