Studies On A New Kind Of Mineral Admixture Of High Performance Concrete

Phenomena such as cracking, abrasive wear, silica-aggregate reaction, freeze-thaw damage, etc., have been effected on some concrete engineering in China due to low tensile strength, large drying shrinkage, liability to influence by the environment of the concrete. Some of the damage has influenced the normal running of concrete structure. Different repairing materials and repairing methods are needed to various engineering defect or damage. It is not allowed to repair by normal ways when construction defects happened to some old concrete engineering or new-built ones, eg pavement, bridge, tunnel, etc. Generally, it is required to be repaired without influence on the traffic, for example, repairing in the night and running in the day. Some engineering works can only be repaired during the several-hour-interval when no running. And some seaport docks need to be repaired during the 2-3 hours of ebb tide time. All these are requiring for special construction methods and rapid repairing materials. Problems such as water leakage and corrosion of water-flow are mostly accompanied in railway tunnel works with longitudinal crack, circular crack, diagonal crack and subsidence, etc. Therefore, it must be repaired combining waterproofing and leak-stopping techniques with structural reinforcement.Based on rapid hardening sulphoaluminate cement, super-high early-strength grouting cement is being developed combining the requirement of rush repairing engineering on injection paste materials with adopting compositing technique, screen separation, addition and optimizing of super-accelerating agent, dispersing agent, set regulator and crack-resistant agent. Its physical and mechanical properties and its durability are being studied in the laboratory. This paper also studied the hardening mechanism of super-high early strength grouting cement through XRD analysis, experiments of electron microscope and porous structure.Compared with traditional grouting cement, it has the characteristics of high fluidity, good grouting ability, quick setting and adjustable setting time. The compressive strength of 30 minutes is up to 10 Mpa and its long-term strength grows continuously. The compressive strength of 28 days is over 50 Mpa. Therefore, the super-high early strength grouting cement studied in this paper is mainly used for rush repairing engineering, for instance, casting reinforcement, leak-stopping and other rush repairing concrete engineering works.Result of the study shows that the super-high early-strength grouting cement has excellent micro-expansivity and can improve the adhesion between the paste and the matrix. In the meantime the hardened paste has good impermeability, sulphate resistance and frost resistance.Result of micro-structural analysis shows that a large amount of ettringite crystal is produced in 30 minutes during the hydration and hardening process, which makes cement paste or concrete generate strength rapidly. With the evolution of hydration, large amount of ettringite crystal continue to produce and grow. Consequently, volume expansion of the hardened paste is generated. Due to the filling of capillary cavity with needle-shaped and bar-shaped crystals, the paste is denser and self-compacting. As a result, the impermeability of the paste is being greatly improved.