Fly Ash Concrete Mixes Research Articles

Modified rule of constant water content for constant consistency of fresh fly ash concrete mixes

Experimental data are presented which suggest that the principle, of ‘constant free water content for constant consistency of fresh concrete’ (Lyse's Rule), which is one of the basic principles for design of normal concrete mixes without fly ash, also applies to fresh fly-ash concrete mixes. It is also shown that the plasticizing effect of fly ash on fresh concrete increases up to an addition of approximately 10% of fly ash by weight of cement, and then remains almost constant for higher contents of fly ash up to an upper limit content, which is defined in the paper.

Modified water/cement ratio law for compressive strength of fly ash concretes

Experimental data are presented which suggest that the development of compressive strength of fly ash concretes can be explained by superposition of two independent mechanical pore-filling mechanisms in the cement—fly ash paste. It is also suggested that the traditional water/cement ratio law for ordinary Portland cement concretes can be applied to fly ash concretes, provided that a slight modification is introduced. This will be of assistance in the design of fly ash concrete mixes for compressive strength.

Modified DOE mix design method for high volume fly ash concretes and controlled low strength concretes

On the basis of some fundamental principles for the design of fly ash concrete mixes,1,2 the Author proposes a number of modifications and extensions of the British DOE method for the ‘Design of normal concrete mixes’. The suggested modifications make it possible to extend use of the DOE method to design of wet lean concretes and controlled low strength materials (CLSM). The properties of both these types of concrete are con-siderably improved by the addition of high volumes of fly ash, but it requires some skill to design high volume fly ash concretes in a logical manner, so that they do show the optimum properties both in the fresh and the hardened state.

Effect of Fly Ash Addition on the Corrosion Resisting Characteristics of Concrete

Reports results of experiments evaluating the corrosion resistance of plain and fly-ash concrete mixes. Variables were fly-ash additions of 0 to 20 percent as cement replacement and four cement contents. Data were developed both for constant water-cement ratio and constant-workability concrete mixes. The corrosion resistance of concrete samples in which fly-ash replaced an equal quantity of sand was also investigated. Samples were immersed in a 5 percent sodium chloride solution for more than 1000 days and corrosion resistance was evaluated by monitoring the half-cell potentials and measuring the corrosion rate of embedded steel using electrochemical techniques. Results show that additions of fly-ash is effective in inhibiting corrosion of reinforcing bars. The corrosion resistance of concrete samples in which fly-ash was used as an admixture seems to be better than those in which it was used to replace cement. The superior performance of fly-ash concrete samples in inhibiting corrosion of reinforcing steel is attributable to the densification of the cement-paste matrix due to pozzolanic action in the fly-ash concrete mixes.

Reaction Products in Fly Ash Concrete

AbstractThe setting and strength gaining process of PC concrete containing Class C high lime fly ash were related to the reaction products identified using XRD and SEM. Four fly ash concrete mixes (20, 30, 40, and 50 percent replacement of cement by fly ash) and similar paste mixes were compared to control mixes for curing periods up to one year. Setting time and early compressive strength were adversely affected by the addition of fly ash. Beyond one week all of the fly ash concrete mixes gained strength at a faster rate than the corresponding control mixes. XRD studies suggest that the retardation mechanism may be associated with the high levels of ettringite formed early in the hydration process and its conversion to monosulfoaluminate. A decrease in the level of calcium hydroxide, typical of pozzolanic activity, was not in evidence. SEM micrographs of fly ash spheres in concrete at the various stages of hydration reveal an intricate crystal framework. A simple heat of hydration test is presented which helps explain the strength gains observed.

Proportioning Fly Ash Concrete Mixes For Strength and Economy

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