Water-binder ratio refers to the ratio of concrete water consumption and cementitious material consumption. Water-binder ratio is an important parameter of concrete mix ratio. Many properties of concrete are directly related to water-binder ratio, such as workability, strength, durability, etc. Water cement ratio refers to the ratio of concrete water consumption and cement consumption. Some of the “experts” in the industry are lumped together.
Generally have activity or potential activity of powder called colloid, cement dosage and water consumption ratio can reflect the strength of concrete and other long-term performance. When other admixtures are added, two concepts of water-cement ratio and water-binder ratio appear. The water-cement ratio represents the strength relationship in the original sense, while the water-binder ratio represents the ratio of colloid to water consumption in slurry. Because the activity index of various admixtures of colloid is different, the water-binder ratio cannot correctly reflect the relationship between the strength of concrete and the water consumption. Concrete mix ratio design must consider the early plastic stage performance and mechanical properties, volume stability and durability. These two stages of the concrete mix ratio requirements are different, sometimes or a pair of contradictions. Therefore, the selection of mix ratio parameters should be considered comprehensively.
1, water cement ratio reflects the mechanical properties of concrete.
Using the different activity index of various admixtures, the amount of admixtures is converted into cement amount, and the effective water-cement ratio is converted, so the strength can be calculated basically. Therefore, the calculation formula of water-cement ratio in the specification is still valid, and the admixture is supergeneration according to the activity index to reach the corresponding water-cement ratio, which can basically guarantee the strength. And consider the following factors:
(1) The activity index of the admixtures is changing due to the interaction between the admixtures. The activity is different with different ages and different blending schemes.
(2) the filling effect of cementing material can be adjusted with different fineness of admixture.
(3) The potential hydration reaction of the admixture may not be fully developed in the specified age, so it can be used as a strength reserve, or it can be considered separately in the concrete to reduce the hydration heat.
(4) For the cementitious material with a certain amount of admixture, it can also be used as the actual compressive strength of the mixed cementitious material by checking the existing cementitious sand strength of the cementitious material with the same amount of admixture (the premise of ensuring the same flow performance) to determine the water-cement ratio in the water-cement ratio formula.
(5) The formula of water-cement ratio should still be applicable to HPC when the influence of activity index of various admixtures is removed.
2. The water-binder ratio determines the durability of concrete
The impermeability is related to the water-binder ratio, and a certain water-binder ratio can meet the durability.
3. The water-binder ratio and the slury-bone ratio determine the working performance of concrete.
By adjusting the proportion of admixtures (even the mud and stone powder in the sand and stone can also be used as admixtures), the water-binder ratio is determined to meet the working performance and ensure that the cementing material in a certain range can not only meet the concrete durability, but also improve the workability. The working performance of different water-cement ratio can meet the design requirements by different amount of admixtures, that is, the influence of water-cement ratio on working performance can be ignored.
4, for different admixtures, their activity index is different, will affect the water-binder ratio, in the fixed age, but can not affect the water-cement ratio. The water-cement ratio and water-binder ratio should be distinguished. The known water-cement ratio can basically determine the strength of concrete. And known water binder ratio and water consumption, can not know the activity index or dosage of admixture, that is, can not know the corresponding concrete strength, but can roughly understand the durability of concrete, working performance. Considering the working performance of concrete in the mix ratio design, the colloid structure design is carried out according to the principle that the durability and working performance determine the water-binder ratio and the strength determines the water-cement ratio. The water-binder ratio can be fixed (in a certain strength range), according to different performance requirements, take different water-binder ratio, that is, the same water consumption and the same total amount of colloid, through different colloid blending rate to achieve different strength grade purpose. Its workability is basically the same. It can also fix the water-cement ratio (under certain working performance), according to different strength levels and different construction methods, take different admixture proportion, to adjust the total number of colloid, to improve the durability and other performance of the purpose. This is also the basic method of high performance of ordinary concrete.
5. How to consider the influence of fine particles in aggregate on water-binder ratio
Aggregate is inevitably mixed with fine powder particles with particle size less than 0.075mm (the use of machine-made sand in Guizhou is more obvious). Although these particles are sometimes not active, they only play a filling role in concrete. In the calculation of water-binder ratio, whether these particles need to be considered, that is to say, whether the increase of these particles will affect the size of the actual water-binder ratio, should be included in the cementing material, control the effective water-binder ratio. The composition of fine powder particles mixed with aggregate is very complex, part of which is stone powder or sand powder, which can play a filling role. But there are also a part of fine mud powder particles, these mud powder particles adsorb water and admixtures, hinder cement and aggregate bonding, reduce the strength of concrete. As a part of the cementitious material, should be treated differently.
Post time: Mar-30-2021