The Rockwell K and F scales were found to be suitable for the hardness determinations. Over a wide range of hardness and strength values, the average compressive strength (fc) varied linearly with the average hardness (RK) according to the relation fc (psi) = 560 RK - 12000, irrespective of casting and curing variables. The weaker materials exhibited greater variations in hardness.
Please share your knowledge.
Dear Raed Ahmad I think the methods can be used for estimation of compressive strength because of assess the only surface properties of concrete. Cores taken from structures could show significantly different compressive strength values unlike its estimations because the surface hardness of concrete members are easily affected by some unexpected problems such as carbonation, freezing-thawing, sulfate attack etc. Your suggested equation can be accurately work in your cases, but i think it should be verifiedwith actual compressive results in-situ applications. Additionally, maybe other non/semi-destructive test methods can be added to reach satisfactory combined equations such as ultrasound pulse velocity, Windsor Probe etc.
Please, look at this article. It may be helpful for your subject to my knowledge.
http://www.sciencedirect.com/science/article/pii/095006188790033X
Hello
Hardness is a property to do with the surface of an object. Surface harness of concrete can be measured using different devices, such as hammer, electronic transducer, etc.
Whereas strength is measured by testing cubes for compressive strength, or beams for flexural strength, or cylinder for tensile strength (slit test).
Best wishes
Hi Raed
Considering for a moment cubes made with cement and water only (i.e grout), it is common cause that as the water-cement-ratio of the mix is reduced, the compressive strenght increases as per the general law of concrete strength, but also the hardness of the cubes (as well as the "brittleness" or more correctly the "flakiness" of the cube surfaces). This relationship between hardness and compressive strength is anecdotally well established (As is claimed in the cited research as well).
It should reasonably be arguable that the same general tendency would hold for "normal" concrete as well, bar the lowering of the hardness of the concrete that might result from low strength aggregate and or air voids in the concrete, which in my opinion might effect the "hardness" of the concrete relatively more than the strength with regards to the possible "ideal" hardness strength relationship of the concrete.
I am sure there should be some more studies in this regard as well, especially for concrete applications where surface strenght/hardness might have been important.
Dear Raed Ahmad:
There is no absolute relationship between the hardness and the compressive strength of concrete due to the reasons mentioned by H. Süleyman Gökçe. The shmedit Hammer still the most used devise for measuring the compressive strength by measuring the surface hardness (the rebound number - R) taking into account all precautions recommended by the manufacturer and the relations drawn on the hammer itself, the percentage of error corresponding to each R value, and the concrete age that would not be less than 14 days and not more than 56 days, outside these age period, Shmedit hammer is good for comparisons only.
Relation between hardness and compressive strength of polymer concrete
By Kisoo Kim and Frederick Milstein
Abstract
Experimental studies were made of the influence of mixing and casting techniques and of curing time upon the compressive strength and hardness of methyl methacrylate based polymer concrete. The Rockwell K and F scales were found to be suitable for the hardness determinations. Over a wide range of hardness and strength values, the average compressive strength (fc) varied linearly with the average hardness (RK) according to the relation fc (psi) = 560 RK - 12000, irrespective of casting and curing variables. The weaker materials exhibited greater variations in hardness. Hardness testing is found to provide a meaningful and convenient method for evaluating the quality of polymer concrete
.....
Article Relation between hardness and compressive strength of polymer concrete
surface hardness tests of concrete can be used for strength estimation using calibration curves. But not to count on for exact determination of the compressive strength of concrete structures. Cores should be taken
Hardness property is based on surface condition of concrete. The surface condition will depends on cement content, water cement ratio, compaction and curing condition. Hardness of aggregate hence type of aggregate will also affect .Higher water cement ratio may lead to rise water at surface due to capillary rise. Hence, proportion of aggregate to cement ratio is also responsible. In short, hardness mainly depends on water cement ratio and strength of concrete. Surface hardness is also affected by environmental conditions. Exact equation between compressive strength and hardness of concrete is difficult to establish due to large number of variables, However, the topic is interesting and more research is needed.
- Badges
- Science topic