Study On The Test Method For Rheological Properties Of Mortars And The Effect Of Chemical Admixtures On The Rheological Properties

Rheology has a great influence on the working performance of mortar. The rheological properties of mortar can be characterized by plastic viscosity and yield stress. As the fresh mortar is a typical Bingham fluid, the flow curve of fresh mortar is a straight line. The Y-intercept is the yield stress, and the slope of the line is the plastic viscosity of the mortar. There are several existing methods for characterizing the rheological properties of the mortar. However, most of these methods can only test one of the rheological parameters, leading to the incomplete evaluate the rheological properties of mortar. Based on a test equipment for the rheological properties of mortar designed by Baoxu Yang, a modified equipment was built. A flow curve could be drawn after measuring the shear rate of the mortar by our equipment. As a result, plastic viscosity and yield stress could be obtained after linear fitting. Moreover, the effect of superplasticizers and retarders on rheological properties of mortars was studied by using our equipment.This paper studies the best applicable conditions of every spout calibers(the diameters are 15mm、18mm、21mm), The effect of spout calibers on the falling time of mortar (800mL) was studied. The falling time of 800mL mortar was used as a judgmental condition, the optimal applicable conditions were showed as following:15mm:T800<7.100s; 18mm: T800<6.071s; 21mm:T800<5.039 s. The smallest size of spout caliber was first chosen. If the falling time didn’t meet the above conditions, a larger mouth was chosen. This paper studied the effect of inner diameters of splice cylinders on the test results. The results showed that the best size is 80mm. The results of our method were verified with mortar coaxial rotational viscosity. In order to make the funnel method more convenient in practical application, the results were analyzed by neural network and linear fitting. The standard deviation of two methods was small, indicating the high accuracy of neural network and linear fitting. Thus, the two simplified methods could be used to predict the rheological parameters of mortars. Moreover, the neural network showed a better accuracy than linear fitting. Thus, the neural network is recommended for the future practical use.The influence of different types of superplasticizers (polycarboxylate, naphthalene or amino) on the rheological properties of mortars was studied by using our method. As the increasing of superplasticizer dosage, the initial plastic viscosities and yield stresses decreased gradually. When the initial fluidity was similar, the mortar with amino exhibited the largest loss rate of fluidity over time, while the mortar with polycarboxylate exhibited the least loss rate of fluidity over time and a small initial yield stress. Furthermore, the mortar with naphthalene showed the middle loss rate of fluidity over time.This paper studied the effect of molecular weight (weight average molecular weight) of polycarboxylates with the same branch density on the rheological properties of mortars. As the increasing of molecular weights, the initial fluidity of mortars increased first and then decreased, while plastic viscosities and yield stresses decreased first and then increased. The superplasticizers with molecular weight less than 118,000 exhibited less loss rates of fluidity than those with molecular weight greater than 118,000.The effect of different types of retarders on the rheological properties of mortars was studied. All retarders could reduce the plastic viscosities and the yield stresses of mortars. The dosages of three retarders had little effect on the yield stress of but great influence on the plastic viscosity. When the mortars had similar setting times, the mortar with sodium gluconate showed a larger initial fluidity, larger yield stress, and less plastic viscosity than the mortar with sugar, while the mortar with sugar had a smaller loss rate of fluidity, plastic viscosity and yield stress than the mortar formulates with sodium gluconate. These results indicated that sugar was favorable for the long-term fluidity of the mortar.