Experimental Study Of Manufactured And In Pre-mixed Concrete

China’s prosperous construction industry utilizes huge amount of sands.Most of the sands used are natural river sands which are accumulated afterlong-year sentiment. However, natural river sands are non-renewablematerials in short term, and long-distance transportation of them also resultsin very high cost. With the rapid development of China’s economy, hugedemands of construction materials due to numerous infrastructure andbuilding projects at a stage of accelerated urbanization has caused theover-extraction of natural river sand. Due to the over-extraction, river sand isin short supply and its quality has dropped in many areas in China, andenvironment is adversely influenced to some extent. In China, On the otherhand, the manufactured sands are very resourceful. Using the manufacturedsand instead of natural river sand not only alleviate the destruction to bothriverbed and ecological system, but also mitigate the shortage of river sandand reduce the cost of construction. This will bring considerate benefits toboth our economy and environment.The main analysis content of this subject.(1) Characteristic study of both manufactured sand and rock powder;(2) Influence of rock powder on the work performance, strength,anti-permeability, contraction and durability of concrete made withmanufactured sand;(3) Influence of manufactured sand on the work performance, strength,anti-permeability, contraction and durability of concrete made withmanufactured sand;(4) Mixing proportion design of concrete made with manufactured sand andits practical engineering application. The main results of this research.(1) The appropriate usage of rock powder filled the voids betweenmanufactured sands, improved the graduation and increased the compactnessof manufactured sands;(2) The appropriate usage of rock powder improved workability andincreased the strength of concrete made with manufactured sand; however,over-usage of rock powder resulted in decreased slump, deterioratedworkability, reduced compressive strength, and poorer performance for bothanti-permeability and contraction;(3) For low to medium strength concrete (C15~C40), the content of rockpowder in manufactured sand should be controlled to be less than9%; forhigher strength concrete (C45~C50), the content of rock powder inmanufactured sand should be controlled to be less than6%;(4) When using both manufactured and natural fine sands to produceconcrete, it was observed that appropriate usage of natural fine sand improvedthe workability and compressive strength of concrete; however, over usage ofnatural fine sand caused the sharp decrement of slump, reduction incompressive strength, poorer performance of anti-permeability, and incrementof contraction rate. E.g. if the rock powder content is5%, the usage ofmanufactured sand should be controlled to range from70%to80%whenusing both manufactured and natural find sands.(5) Benchmark mixing proportion design for C15~C50mixed-sandpremixed concrete was performed. The mixing proportion coefficients weresystematically varied, and the relationship between rock powder content andmanufactured sand content in mixed sands (including manufactured andnatural fine sands) was obtained.