Capping of Light weight concrete

[essam480]

Hello everybody

I'm a technical manager in a geotechnical consulting engineers. Recently, we have a lightweight concrete mix design. Unfortunately, our technician forgot the capping of the samples before 7 and 28 days testing. The results are as follows:

7-Days:

1- 128 Kg/cm2
2- 135 Kg/cm2
3-132 Kg/cm2

28-Days:

1-115 Kg/cm2
2-110 Kg/cm2
3-105 Kg/cm2

What's the reason?

 

[Ron]

You have not given adequate information for the evaluation of such a problem. Is this a lightweight structural concrete? If so, what is the anticipated 28-day strength? Unless you have an intentionally low strength mix design, all of these results are lower than would be expected for a structural lightweight concrete having an anticipated 28-day strength of 200+ kg/cm2.

Consider sample disturbance.

 

[Hoaokapohaku]

Some questions:

Were both the 7 and 28 day results molded from the same batch?
Were these lab mixed samples or plant mixed?
Were both sets subjected to the same curing?
Was standard or field curing used?
Did the same technician mold both the 7-day and 28-day specimens?
How long after the concrete was batched when the specimens were molded?
Were all specimens molded within the specified time limits?
How was the light weight achieved? Are there any potential deleterious reactions between mix components?

There are many more relevant questions but let's see if any of these help first.

 

[bb29510]

remember light weights are not moisture cured

ICC special inspector, Structural masonry, Reinforced concrete.