Effect of addition time of a superplasticizer on cement adsorption and on concrete workability

Effective low-energy mixing procedure to develop high-fluidity cementitious pastes

“…By now all these 3 methods are the same particularly the first and the third methods which shows almost the same results but in M.2 after the dispersion process of cement particles a percentage of water, which seems do not engaged in reaction with cement entirely, remain as a free water resulting a higher fluidizing effect and consequently lower outflow time thus proving its superiority among the other methods. These findings also are in agreement with the results reported in previous studies [14,15] demonstrating the effectiveness of delayed addition time of SP to cement. Furthermore, it can be understood that the stepwise and delayed water addition is also an efficient method with respect to higher fluidity as studied in this research work.…”

“…It was found that the best fluidizing effect could be acquired after adding 70% of mixing water to the cementitious materials and mixing for 3 minutes followed by adding the optimum dosage of SP and mixing for at least 4 minutes, 6 minutes seems preferable based on visual assessment, and finally adding the remaining 30% of water and blending for an extra 6 minutes to reach a steady-state consistency. However, the findings of this paper confirm the efficiency of delayed SP addition method, reported in previous studies [14,15], they also demonstrate the effectiveness of delayed and stepwise water addition method as the main contribution of this paper. This provides the possibility of reducing the paste water content resulting in higher strength and durability or even, with the same w/c ratio, causes an improved workability or the possibility of increasing the aggregate content leading to a costeffective and eco-efficient UHPC.…”

“…The all three methods are similar in such a way that the SP is mixed for 10 minutes after its introduction to the mix to reach a steadystate consistency. Moreover, in all the 3 methods based on the findings for highest SP efficiency [14,15], in which the effective time of SP addition is around 150 seconds after watering the cement, water and cement mixed for 3 minutes and then the SP was introduced.…”

“…According to this study, as time elapses, the C 3 S and C 2 S are consumed and C-S-H gels are gradually formed and the number of positive particles, adsorbing the SP chains, reduces. In this regard, the addition time of SP with respect to highest fluidity is during the first 15 minutes after adding water to cement and particularly between first 2 and 3 minutes [14]. Another recent experiment also confirms that stepwise and particularly delayed addition of SP, which mean adding SP in two stages and also not adding all the SP with water at the beginning respectively, could improve the flowability of UHPC by more than 25% compared to direct addition of SP with or immediately after water addition [15].…”

Determination of relevance between surface free energy and adsorption capacity of cement particles

“…KIMA B G et al [6] showed that the cement containing low amount of soluble alkali have a tendency to adsorb a high amount of superplasticizer, while the cements containing high amout of soluble alkali do not. CHIOCCHIO G et al [7] and HSU K C et al [8] found that The fluidity of portland cement pastes is greatly affected by the time of addition of the superplasticizers. When the addition of superplasticizer is delayed the workability is always found to be higher.…”