The Influence Of Ultra Fine Sand On Rheology Of Self-consolidating Cement Mortar

Nowadays,the accumulation of ultra-fine suspended sediment(UFS)in estuaries is considered as one of the most serious environmental problems.Although a few studies have shown the possibility of using estuarine sediments in civil engineering applications,there is very little information on the effect of UFS on self-compacting mortar(SCM)performances.To compensate for the deficiency of natural sand(NS)resources,decrease the accumulation of suspended sediments and promote the utilization of ultra-fine sand(UFS)from Changjiang estuary,therefore,this study aimed to evaluate the feasibility of using the UFS as a partial substitution of mediumsize sand by up to 50% and as cement up to 30% in the production of environmentally friendly self-consolidating mortar(SCM)while underlying its rheological properties.Wet packing density,fluidity(mini-slump flow and V-funnel flow time)and rheological(viscosity and yield stress)properties of SCM mixtures were assessed.Furthermore,the impact of UFS on the compressive and flexural strength of SCM mixtures was investigated at different ages.A calorimetry test was also conducted to evaluate the role of UFS as a pozzolanic material in SCM mixtures.With UFS filler technology,this paper depicts SCM thixotropy behavior by shear thinning index,compare wet packing density with its fluidity,rheology and strength creatively,use regression functions to analyze the correlation between UFS replacement ratio and SCM rheology,wet packing density and strength,so then a UFS replacement ratio satisfied to SCM for the sake of each parameter was given.The data mainly indicates that:(1)The fluidity of SCM would pace together with the evolution of its wet packing density.For as the medium-size sand replacement,the fluidity decreased fi rst while increased later and have the minimal wet packing density at 30% UFS replacement ratio,which was the minimal fluidity;For as cement replacement,there existed a maximal wet packing density at 5% UFS replacement ratio,which was the maximal fluidity,then the fluidity decreased later with higher UFS ratio.The SCM mixtures meet adequate self-compacting characteristics basically in accordance with EFNARC limitation.For the sake of fluidity,the replacement ratio of UFS should be within30%.(2)The time-dependent rheological parameters of SCM increased with a higher UFS replacement ratio.With the lapse of time for 1h,viscosity achieved dynamic equilibrium after its increment for 30 mins and the yield stress ha d a sustained growth when as the sand replacement,while two rheological parameters would increase continuously when as cement replacement.Moreover,duration time and UFS replacement ratio are both positive correlat ed with the time-dependent rheological parameters.Basically,rheological parameters are more sensitive to changes in time.(3)The SCM mixtures with USF replacement perform as pseudoplastic fluid.In two kinds of replacement situations,when the replacement ratio of UFS increases,the shear sensitivity index n and consistency index K would both increase,so as the thinning index TI,which indicates higher thixotropy.And there exists a significant increment in it with the ratio higher than 30%.For the sake of stable thixotropic behavior,the replacement ratio of UFS should be within 30%.(4)The replacement of UFS as cement would retard mortar hydration.The calorimetry data prove that UFS in SCM mixtures acts as non-hydraulic fillers instead of a pozzolanic one,but it could offer excess nucleation sites and then offset both compressive and flexural strength reduction at 7d-30% compared to 7d-0% at later hydration stages.When the replacement ratio is in 5%-15%,the strength of these mixtures could reach 85% of their control mixtures.Wet packing density and strength of all mixtures at each age are positively correlated.A mixture with a wet packing density above 67.05 could meet its design strength.For the sake of strength,the replacement ratio of UFS as cement should be within 20%.