BP Network Based Mix Proportion Design of Self-Compacting Concrete
It was known that many parameters of raw materials, such as, strength of cement, mud content and modulus of fineness of river sand, maximum size of aggregate, content of' needle-like/sheet-like crushed stone, loss of ignition and fineness of fly ash, may exert significant influence on the theology and mechanical properties of self compacting concrete(SCC). It is a dream of researchers to identify the influencing degree of various factors on performance of SCC so as to obtain optimal properties. By virtue of BP neural network approach, this paper employed strength of cement, mud content and fineness modulus of fineness of river sand, maximum size of aggregate, content of needle-like/sheet-like crushed stone, loss of ignition and fineness of fly ash as the input parameters, and the corresponding optimized mix proportion as the output to describe the nonlinear relationship between them. And the orthogonal experiment was designed for the purpose of training and verification of network. The results demonstrated that the pre-trained BP neural network trained by orthogonal test data may employ to predict the optimal concrete mix proportion. This approach may replace some waste-time and heavy laboratory tests. In addition, such method may real-time optimize mixture proportion. of self-compacting concrete, which has great effect on the quality control of manufacturing self-compacting concrete.
Experimental and numerical studies in self-compacting concrete
This thesis describes the steps taken to develop normal strength (30-80 MPa) selfcompacting 
concrete mixes with 20mm maximum size aggregate. For the selfcompacting 
concrete mixes with 20mm maximum size of aggregate fulfilment of the 
flow and cohesiveness criteria are found insufficient for the mix design. It is found that 
they must additionally meet the passing ability criterion. 
A Lagrangian particle based method, the smooth particle hydrodynamics (SPH), is used 
to simulate the flow of SCC mixes. An incompressible SPH method is employed to 
simulate the flow of such non-Newtonian fluids whose behaviour is described by a 
Bingham-type model, in which the kink in the shear stress versus shear strain rate 
diagram is first appropriately smoothed out. The basic equations solved in the SPH are 
the incompressible mass conservation and Navier-Stokes equations. 
The yield stress of SCC mixes is predicted in an inverse manner using the SPH 
simulation methodology and matching the measured and simulated t500, tstop and the 
final spread of the cone flow test. It is found that the yield stress of SCC mixes varies 
only slightly with an increase in the characteristic compressive strength of the mix. The 
plastic viscosity on the other hand shows a marked increase. The latter was estimated by 
a micromechanical procedure proposed by Ghanbari & Karihaloo (2009) based on the 
measured viscosity of the cement paste alone and on the volume fractions of the mix 
constituents. 
The SPH simulation methodology was also used for predicting the distribution of large 
coarse aggregates in the cone spread. This distribution was found to be indeed very 
similar to that revealed in the cut sections of the hardened test cone spread. These large 
coarse aggregates had been painted with non-toxic non-water soluble paints prior to 
being used in the test mix. 
The simulation of SCC mixes revealed that the cone lift rate in the slump flow test has a 
significant effect on the flow pattern and the measured t500. The latter decreases as the 
cone lift rate increases from 0.1 to 1 m/s. The effect on the spread (i.e. tstop) is, however, 
insignificant.
TESTING HIGH-STRENGTH CONCRETE COMPRESSIVE STRENGTH
Comparative testing reveals that high strength concrete (HSC) compressive strength values are greater by 5% when measured on 100 x 200 mm specimens. Moreover, the coefficient of variation on one set of three 100 x 200 mm specimens is as small as, or smaller than that for 150 x 300 mm specimens. Furthermore, a high performance capping compound testing 60 to 70 MPa using 50-mm cubes has proved to be effective when used for testing HSC up to 120 MPa due to the confinement of the capping compound between the platen and the specimen, but the capping layer has to be less than 3 mm thick. Under these conditions, the results are similar to those obtained when the ends are faced by grinding. Nevertheless, it is safer to grind the specimen ends when the strength of the concrete exceeds 100 MPa. It is shown that eccentricity of less then 4 mm between the testing machine and specimen axis does not affect the compressive strength values.