SummaryThis technical report presents the findings of concrete tests done with samples casted using PFA as a partial replacement for cement. The samples exhibited good mechanical properties desired for structural concrete, in addition to improving some of the concrete properties. The characteristic strengths of the samples containing PFA are exceptionally high and can be used in structural design. IntroductionWell cured and hardened concrete material has to be strong enough in order to be able to withstand all the structural and service loads intended to be applied to it. It must also be sufficiently durable to withstand the environmental conditions for which the structure is designed.
Using high quality materials that are well mix-designed, handled and well placed and finished ensures that the concrete material produced attains high strength and becomes durable when used in structural building (Dhir, et al. , 2002). Properties of hardened concrete include: workability, creep, shrinkage, water tightness, strength and rate of strength gain, durability, and Modulus of Elasticity. These concrete properties depend on the mix design (mix proportions), the curing conditions and the environment (Shirley, et al. , 2009). Concrete strength generally refer to its compressive strength, because concrete is very strong in compression and relatively weak in tension.
Concrete compressive strength largely depends on the amount of cement used, the water-cement ratio, aggregates, curing conditions, age, and admixtures used (Thomas, 2007). A lot of research has been ongoing to address some deficiencies of concrete, with some providing very significant efforts geared towards improving its structural performance. The existing literature shows that partial replacement of cement using mineral admixtures can significantly reduce the porosity and improve the density and durability of concrete, alongside improving the compressive strength, flexure and tensile strength.
A part from enhancing concrete’s ability to exhibit greater resistance against harmful chemical attack and environmental conditions, mineral admixtures significantly contribute to sustainable environment as partial replacement of Portland cement and are normally referred to as “ less energy intensive” cementitous materials (Thomas, 2007). Among available mineral admixtures, the most commonly used are pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS), silica fume (SF), rice husk ash (RHA) and metakaolin (MK) (Khatib, 2009). PFA has also worked well and recommended for structural use as a partial replacement of fine aggregate.
This report presents the results obtained for density, compressive strength test and RC beam test for Self compacting concrete (SCC) samples tested using standard methods. The concrete cubes and cylinders were prepared by designing and batching a concrete mix using Pulverized Fly Ash (PFA) as a partial replacement of cement. Experimental MethodInitially, 0.035 m3 of concrete trial mix was designed using the BRE method to the specifications on page 2 and 3 of the lab manual for a test age of 28 days.
VMA compounds and super plasticizer were added to the concrete sample to produce the SCC mix. From this mix, 3 concrete cubes were prepared using cubical molds with a length of 100mm, and another 3 cylindrical concrete samples were prepared using cylindrical molds 100mm diameter and 200mm long. The masses of hardened concrete samples were measured and then the cubes tested for compressive strength using the Schmidt rebound hammer after the 28 day period of curing under a tank of water. An ultrasound of equipment was used to determine the value of elastic modulus of the concrete, and hence, its compressive strength as well.
The samples were then tested for compressive strength using a destructive method under increasing load, and the maximum load at failure and the modes of failure recorded. Reinforced concrete (RC) beam was prepared by making a reinforcement cage to the bar schedule drawing in the lab and then placing it in a reinforced concrete mold measuring 1.5m by 100mm by 200mm. The beam was set as shown in the figure below.