On Concrete Workability And Durability

Concrete mix design includes workability-design,strength-design and durability- design. The present theories and test methods are both not perfect. For example,concrete durability-design relies mainly on complex special testes,e.g. thawing and freezing test and permeability resistance test etc. On theories and test methods of workability-design,testes for Theological properties of concrete,workability evaluation,determination of optimum dosage of water-reducer etc -are all depend on experimental methods. With mortar being separating matrix,from aspects of theories and test-methods of workability-design,separation mechanism of water-reducer for cement paste,relation between properties of interfacial zone and concrete durability etc,this work focused on sample index for durability evaluation,saturation dosage of water-reducer,test for rheological properties of mortar and test on concrete workability etc,achieved following main conclusions.1. Failure probability of coarse aggregates (PFCA) could be a sample index durability evaluation of concrete in compressive strength test,where PFCA was the ratio of number of total particles to which of the broken ones of coarse aggregates in the failed faces of a concrete specimen. The value of PFCA was a denotation of properties of the weakest part,viz. interfacial zone between cement paste and aggregates in concrete,The PFCA was a function of void structure in interfacial zone.2. Workability-design of fresh concrete was studied from rheology aspect.Mortar slump flow test was further developed to evaluate properties of water-reducers and compatibility between cement and water-reducer for mortar. A method for measuring water absorbed by coarse aggregate in fresh concrete was put forward. Saturation dosages of two plasticizers in concretes were measured by bar-slump test. A mathematic model for calculating saturation dosage of plasticizer in concrete from which in mortar was found out by taking adsorption of coarse aggregate into account.Cone-based rheometer was modified to estimate the rheological properties of fresh mortar,which can measure yield stress and plastic viscosity of mortar in relative units. Effects of many factors on rheological properties of mortar were studied. A set of test theory and method for designing rheological properties of mortar was recommended.Study on workability-design of fresh concrete was carried out by introducing coefficient of filling-voids of mortar (CFVM),where CFVM was the ratio of voids content of densely packed coarse aggregates to the volume of mortar in concrete. Adopting different CFVM concretes with different workability were achieved while the same proportioned mortars and the same kind of coarse aggregates were used.3. Measures for further developing concrete mix design were presented based on above work. For example,adopts PFCA as an index in designing durability of concrete,uses mortar slump flow test to select cements and water-reducers and to measure saturation dosage of water-reducer in mortar and then determine optimum dosage of it in concrete,uses bar-slump test to determine stability and fluidity of fresh concrete,and consequently,the workability of high fluidity and high stability concrete such as pumped or self-compacting concrete can be designed by adopting proper CFVM determined in terms of rheological properties of designed mortar measured with cone-based rheometer.