Question : How does retarding admixture effect to fly ash concrete?   

Answer : All admixtures containing retarding absolutely affect to concrete properties particular in setting time, and also others physical properties such a bleeding rate and segregation. Most retarding admixture will affect to longer set of cement hydrated depending on dosage rate. Particular in high volume of fly ash in concrete is significantly much affect both longer set and risk of bleeding occurrence. So users should aware of correct dosage to fly ash concrete. By theoretically, retarding admixtures are recommended to use max. 500 ml per 100 kilogram of cement depending on type D or mid-range.

Question : How to use superplasticizer admixtures in correct way?   

Answer : Before using superplasticizer admixtures, user should understand 2-3 relevant factors of them. Firstly, in mixing process normally superplasticizer should put in after mixing water into cement in few seconds. In practically, it might not able to control under saying. The different outcomes between mixing admixture with water and after water mixing probably differ slightly but in significantly. Secondly, mixing time should take at least 90 seconds per batch in order to get better homogeneity. Finally, how to teach operation level to understand and practice in correct way, also transfer to contractors later.   

Question : How to inspect the admixture properties?  

Answer : There are generally 3 methods to inspect the properties of chemical admixtures. The first method is called physical properties e.g. specific gravity, solid content, pH, viscosity and physical properties. The second method is called concrete properties e.g. percentage of water reduction, strength index, time of set. The last method is called chemical properties or chemical composition analysis which it has limit of Thai institution both personal and equipment aspect, so most of them are necessary to inspect aboard.   

Question : How to accelerate concrete with short period e.g. concrete slip form or fast set owing to the limitation of the amount of formwork?   

Answer : It can adopt cement type III for developing early strength or use admixtures type F without retarding effect. Then concrete should minimize water-to-cement ratio or control lower slump. However, there is the another option to use hardening accelerator admixture type combination with superplasticizer to rapid set time of concrete.

Question : How to choose a proper form release agent with concrete?

Answer : There are major two kinds of form release agent: water base and solvent-oil base. Water-base type can apply for concrete casting in roof-protection factory. There are two types of water base: ready-to-use and diluted with water in concentration. The another type is solvent oil-base that can be applied both in-door and out-door factory. The advantage of oil-base is against rain environment after applying on formwork. Moreover, some are blended with second-grade oil to reduce its cost.