Relation between Modulus of Elasticity and Compressive Strength of Ultrahigh-Strength Mortar with Mixed Silicon Carbide as Fine Aggregate

Ultrahigh-strength mortar mixed surface-oxidized silicon carbide as a fine aggregate was prepared by means of press-casting followed by curing in an autoclave. The relation between modulus of elssticity up to 111 GPa and compressive strength up to 360 MPa of mortar mixed silicon carbide was discussed and it was revealed that the contributions of the aggregate hardness and of the interfacial strength between the aggregate and the cement paste on the elasticity of mortar were imporant.

Effect of Quartz Particle Size and Cement Replacement on Portland Limestone Cement Properties

This research focuses on investigating the effect of quartz particle size and cement replacement on their physicomechnical properties.Portland limestone cement(PLC)was employed and replaced with quartz powder(QP)at various particle sizes(1.19 mm,425μm,300μm,212μm,<212μm)and cement replacement between 2.5 wt.%~15 wt.%at interval of 2.5 wt.%to study their impact on the cement properties.The PLC chem­ical composition revealed a relatively low lime and high silica content compared to the conventional cement.QP revealed a high silica,lime and sulphur contents compared to natural sand.A high consistence,elongated setting times and lower strengths and specific gravities were observed as cement was replaced with QP at a given particle size respectively.The effect of replacing cement with QP content between 2.5 wt.%and 15 wt.%at various particle sizes resulted in average increments by 45.32%,23.13%and 36.06%for initial setting time,final setting time and water demand respectively.This increase could be related with clinker diminution cou­pled with enhanced QP surface area and clinker diminution.Similarly,an increase in the QP surface area at a given cement replacement led to higher water consistence,retarded setting times and lower strength.The effect of enhancing the QP’surface area between 1.19 mm and below 212μm at a given cement replacement resulted in average increments by 26.27%,8.61%and 7.49%for initial and final setting times and water demand respectively.The strength gain of the QP cement blend diminished significantly above 30%up to 15 wt.%cement replacement especially beyond 3 days.The low strength could be due to the high-water consistence linked with silica con­tent resulting in setting time retardation.The optimal QP content was deter­mined at 5 wt.%owing to the fact that the physicomechnical properties did not significantly deviate from the properties of control.

Characterization of Manmade and Recycled Cellulosic Fibers for Their Application in Building Materials

The aim of this study was to characterize two types of cellulosic fibers obtained from bleached wood pulp and unbleached recycled waste paper with different cellulose content(from 47.4 percent up to 82 percent),to compare and to analyze the potential use of the recycled fibers for building application,such as plastering mortar.Changes in the chemical composition,cellulose crystallinity and degree of polymerization of the fibers were found.The recycled fibers of lower quality showed heterogeneity in the fiber sizes(width and length),and they had greater surface roughness in comparison to high purity wood pulp samples.The high purity fibers(cellulose content>80.0 percent)had greater crystallinity and more homogeneous and smooth surfaces than the recycled fibers.The presence of calcite and kaolinite in all of the recycled cellulosic fibers samples was confirmed,whereas only one wood pulp sample contained calcite.The influence of the chemical composition was reflected in the fiber density values.Changes in the chemical composition and cellulose structure of the fibers affected the specific surface area,porosity and thermo physical properties of the fibers.More favorable values of thermal conductivity were reached for the recycled fibers than for the wood pulp samples.Testing the suitability of the recycled fibers with inorganic impurities originating from the paper-making processes for their use as fillers in plastering mortars(0.5 wt.%fiber content of the total weight of the filler and binder)confirmed their application by achieving a compressive strength value of 28 day-cured fiber-cement mortar required by the standard as well as by measured more favorable value of capillary water absorption coefficient.