Air content self consolidating concrete
This was especially the case for concrete with low water-to-binder (w:b) ratio of 0.33. In turn, Emborg noted that the robustness is also a function of the mixer volume and in industrial full scale mixers, the variations in properties are smaller than those produced by laboratory mixers. The effect of delayed addition of SP on the slump flow and V-funnel time was studied by Domone and Jin.[i] In their study the delay in the time of addition of SP varied from zero to 6 minutes in increments of 1 minute. 8 shows the mixing sequence in which the powder, sand and 80% of the water were mixed for 2 minutes and then the SP and 20% of the water were incorporated. Mixing sequence adopted by Domone and Jin Three types of superplasticizers were used: naphthalene-based SP, melamine-based SP and polycarboxylic ether-based SP. The increase in paste volume is also shown to reduce the plastic viscosity of SCC. and Asaga, K.,” Rheological properties of cement mixes: III The effects of mixing procedures on viscometric properties of mixes containing superplasticizers,” Cem. It was observed that delayed addition increased the fluidity of the SP as measured by both the flow spread and V-funnel flow time.
In addition, the mean interparticle distance play a significant role on the flow characteristics of SCC as it affects the rheological properties and the capacity to flow through obstacles. The pugmill mixers typically consist of a horizontal drum and one or two rotating horizontal shafts with attached blades. using a gravity mixer (G) and a forced paddle mixer (F). and Mouret, M.,” Study of the shear thickening effect of superplasticizers on the rheological behaviour of cement pastes containing or not mineral additives.,” Cem.
Higher aggregate content increases the yield stress and viscosity, so does aggregate with high aspect ratio.[xii] Similarly Assaad and Khayat[xiii] showed that an increase in the coarse-to-fine aggregate ratio and an increase of size of aggregate bring about a significant increase in the rate of stiffening. The effects of the superplasticizer:binder ratio (by wt.) on slump flow of concrete at w:b ratio of 0.39 (Bonen and Shah) Bonen and Shah reported on the effects of the superplasticizer content, coarse aggregate-to-cement ratio, and fine aggregate-to-coarse aggregate (c:f) ratio on the flow properties of concrete. Forced pan mixers have higher mixing efficiency than drum or mortar mixers (Deshpande and Olek,[iv] and Takada et al.). performed laboratory investigation of the effect of mixer type on fresh concrete properties of SCC and concluded that for the same composition and mixing sequence, tilting drum mixer increases the V-funnel flow times of SCC as compared to SCC mixed in pan mixer, and to achieve the same slump flow (650±30 mm), smaller amounts of superplasticizer (SP) were needed in the tilting drum mixer. It was reported that for the same water-to-powder ratio by volume (Vw/Vp), longer mixing times for 7.5 and 3.5 minutes in gravity mixtures required lower SP dosages and resulted in higher slump flow values and low V-funnel flow times as compared to shorter mixing times of 5.5 and 2.5 minutes.
It was shown that for any content of superplasticizer-to-binder (SP:b) ratio, the slump flow increases as the aggregate-to-binder (agg:b) ratio decreases (Fig 1). G., “A viscometric study of cement pastes containing superplasticizers with a note on experimental techniques,” Magazine of Concr. By contrast, SCC produced in pan mixer was found to be prone to changes, which compromised the robustness of the mixtures. Mixtures with the same w:p volume ratio were mixed in a mortar mixer and a conventional laboratory pan mixer. "Effect Of Mixing Equipment And Mixing Sequence On Rapid -Setting Self-Consolidating Concrete." pp. However, in the case of forced pan mixers, in order to obtain the same degree of deformability, mixtures that mixed for 5 minutes required higher dosages of SP than the corresponding mixtures with the same Vw/Vp that mixed for 3.5 minutes.
Similar to the fluidity, the viscosity is readily changed by changing the superplasticizer and aggregate contents (Fig. The effects of the latter on viscosity cannot be overlooked as the effects are as important as the role of superplasticizer. The optimum addition time ‘window’ was found to be 2 to 4 minutes for the naphthalene- and melamine-based admixtures, but 0 and 0.5 minutes for polycarboxylic-based admixture. A.,” Mathematical model for the flow curve of cement paste,” Magazine Concr.
The figure also shows that the effect of aggregate on viscosity is exponential. Deshpande and Olek prepared 27 mixtures of RSSCC and found that the time in which the superplasticizer was added affects the rheological properties.
Carlsward, et al.[ix] have studied the effects of entrapped air, silica fume, limestone, and moisture on the rheological properties. "Flow Stabilizing Properties of Special Viscosity Agent." The 37th Japan Congress on Materials Research. [v] Nishizaki, T., Kamada, F., Chikamatsu, R., and Kawashima, H.; (1999). top Emborg[i] concluded that the properties of SCC are more sensitive to both, deviation from the designed target and mixing technique. G.,” An experimental study of the effect of pfa on the rheology of fresh concrete and cement paste,” pp 161-171 in Proceedings, Intern.