ASTM has updated the following tests:
C231-04 Pressure Meter
C172-04 Sampling
C143-05 Slump
C1064-05 Temperature
I'm wondering if there are any significant changes in these
tests. Usually the changes are minor,but in 2001 they radically changed the procedure for the roller meter. Any...
There are a number of admixtures available with classification of HRWR -High Range Water Reducers (Superplasticizers) that have NSF approved status. NSF certifies most concrete components such as cement, flyash, slag or admixtures can be used in potable water applications. NSF is a U.S. based...
The truth of course is that neither accurately reflects the strength of insitu concrete. Both standards for acceptance or rejection purposes require that the specimens be cured in a moist condition under ideal temperature i.e. 70 degrees F. This procedure will indicate the potential strength...
All response posters are correct but I think Stephen is right on the money, especially when looking at in-situ strengths. Mass traps heat and heat cures concrete, hence strength develops much quicker in a massive concrete beam than it might in a 6" cube or cylinder. An excellent tool to...
It is my opinion that taking one core and cutting it into three specimens does not best represent an average of the in-situ strength of the concrete member. Your objective would be better served by random sampling core locations and then averaging the results. As to why the actual strengths...
In Contrast with techmaximus, I have seen plenty of low strengths that were attributed to poor sampling technique or poor initial curing or early cylinder handling. One can avoid the marginal quality readymixed concrete suppliers by specifying that the concrete supplier must ship from a NRMCA...
In my experience, with numerous DOT's, they usually have a list of approved suppliers which would include cement, admixtures, aggregates and concrete. The materials are tested well in advance and testing is usually done by AASHTO approved labs. Minimum Cement contents are generally higher than...
A excellent resource for concrete knowledge is available from your local portland cement manufacturer. Typically this is a free service available to users of portland cement. Given that ready mixed concrete and/or precast concrete contains high volumes of portland cement, this service is there...
If you are placing concrete and weather reports indicate snow is coming or if the temperatures at at or below 32F, you need to protect the concrete from freezing. The water in the concrete mix will freeze and thaw and expand and cause cracking and disruption of the cement aggregate paste. Not...
To try to explain why three parts of the same coring may exhibit wide variation, I would suggest that in-situ strength is a function of time and temperature. Since mass traps heat and heat cures concrete, one would expect higher peak heat closer to the core of the concrete member and this would...
In addition to Ron's advice, I would suggest that Type V Portland is in very short supply throughout the U.S. An alternative would be to use a Type II plus enough slag cement to give you the chemical composition of a Type V cement. Typically a mix design with Type II Cement and 50% slag cement...
Using a percentage of design strength allows for the use of performance based concrete mix designs, which is the better alternative. Performance based mix designs allow suppliers to design mixes that will achieve higher ultimate strengths, lower maintenance costs and extend the life cylcle of...
The members have provided a great deal of insight as to what might have contributed to your "blow out" problem. I have seen PT contractors use 'field cured cylinders' to determine when PT operations should commence. There can be huge differences between the strength of field cylinders and the...
What I want to see is a letter from the concrete supplier with the proportions of each raw material, giving both weights and volume occupied. The weights should be based on materials in a S.S.D. (Surface Saturated Condition). It should also list sources of raw materials. Each mix design being...
A swiss hammer is quite useful as a paper weight on my desk. It is a useful tool to measure uniformity of strength on a single concrete member. The test is subjective at best and almost any result you want to get, you can get. That makes it the least expensive, all time favorite of the...
