Concrete flowability

Portland cement concrete, flowable fill, and asphalt paving applications... 

It should be reminded that concrete flowability decreases with temperature. Surprisingly, the stiffening ocenrs more rapidly in the case of mixing concrete mixture than with no mixing [378]. 

In a t5 ical concrete mixing process, a large amoimt of water is added to increase flowability of the concrete (23). However, a water overdose lowers concrete compression strength and adversely affects other properties. In contrast, a lack of water causes concrete slump and deterioration, which is harmful to a construction process. Many chemical additives have been described to improve the concrete flowability without the need for increasing the amount of water. 

These additives, even at a relatively low additive level, can provide an improved water reduction, increase concrete flowability, reduce concrete slump and enhance compression strength (23). 

Flowable fill is defined by the American Concrete Institute47 as a self-compacting cementitious material that is in a flowable state at placement and has a compressive strength of 8.3 MPa (1200 psi) or less at 28 days. Most current applications for flowable fill involve unconfined compressive strengths of 2.1 MPa (300 psi) or less, which makes possible its excavation at a later date. 

The types of water-soluble polymers used for the thickening cement slurries, mortar and concrete are shown in Table 6.6. Although many polymers shown in Table 6.6 can be used to increase the viscosity of the water in the mix, they are not all pseudoplastic polymers compatible with cement systems. Only a few can be consistently combined with water-reducing admixtures (WRAs) and superplasticizers to produce concretes with cohesive yet highly flowable mixtures [40, 41, 43]. 

Non-dispersible concrete can be poured into a water-filled form without a tremie pipe to produce dense structural repairs. This type of material has particular advantages over conventional concrete both in terms of the quality of the repair produced and the reduction in placement cost associated with plant and diver manpower requirements. Field tests carried out on a commercially available AWA[46] show that bonding capability, pumpability and flowability around reinforcement are improved over conventional tremie-placed concrete. The quality and strengths of cores show AWA concrete to be suitable material for in situ structural concrete construction at considerable water depths [46]. 

LMC is used in underwater concrete for both new construction and repair. The important requirements to obtain antiwashout capability, such as segregation resistance, flowability, self-leveling characteristics and lower bleeding are provided by the addition of viscosity-enhancing polymeric admixtures at polymer-cement ratios of 0.2-2.0%. These admixtures are water-soluble polymers, and classified under two groups, viz., cellulose types such as methyl cellulose and hydroxy ethyl cellulose and polyacrylamide types such as polyacrylamide and polyacrylamide-sodium acrylate [101]. 

The production of concretes with very high flowability where the admixture is added to the mix with no alteration in water-cement ratio to produce slumps in excess of 180 mm. 

With the advent of high-performance concrete and the development of third-generation (mostly acrylic polymer-based) superplasticizers which provide significantly higher water reduction at flowable consistencies, this demarcation has blurred. Through the use of a mixture of admixtures it is now possible to obtain highly durable low water-cement ratio concretes that are nearly self-leveling and yet quite cohesive. 

Concretes containing VEAs have consistencies that are structured while static but become highly flowable, with self-leveling characteristics, when work is imparted to it. Data presented in Fig. 7.28 show that medium-strength concretes with equal slumps perform very differently in the washout test. This indicates that the slump test does not correlate to washout... 

The quality and strength of tremie concrete is greatly dependent on proper mix design and placement. They should posses good cohesion and flowability. Concretes used for this purpose are usually cement rich... 

Combinations of VEAs, WRAs and SPs are used in controlling sedimentation in highly flowable slurry like concrete and in underwater concrete used... 

Concrete Additives. Melamine-formaldehyde resins can be sulphonated and then used in fresh concrete to create a plasticizing effect. The resin makes 1) concrete more flowable, thus improving concrete s workability and 2) allowing the water content to be reduced for faster drying times. The end result is an improved, stronger material that is structurally superior. 

In general, results of different types of tests are not correlated. Compared with the slump test, flow tests are more suitable for flowable concrete, while the compacting... 

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