Sole of Concrete—Mix Proportion - The Issues and Discussion of Modern Concrete Science - page 5

p

d=D

3

P ¼ 100 ð 1 : 2 Þ

Material which is comprised of small and big particles will only obtain maxi-
mum density, and minimum void content will only be obtained if the particle
grading conforms to the Fuller curve. In China, requirements for concrete aggregate
grading in many industrious construction speci cations are formulated on the basis

of Fuller curve and made proper amendment considering specific situation of
China. The Chinese

Mix Design Speci cation for Highway Pavement Concrete
adopts the maximum density method as theoretical basis.

1.1.3 Weymouth Grap Grading Method

Weymouth held the view that small particles with adjacent diameter would bring
adverse impact to the skeleton formed by larger particles. Meanwhile, studies
conducted by Professor Lian Hui-zhen of Tsinghua University in China believed
that small particle could only

fill the voids in skeleton formed by larger particles
and would not play a negative role in increasing aggregate void content if the
diameter of small particle was nearly one-sixth of the larger particle. In order to
avoid bringing adverse effect to void content and concrete strength, it is needed to
adjust the proportion of the small and large particles to form gap grading manually.
Guided by this idea, coarse aggregates in concrete are usually single grading
rather than dual grading. That is to say, coarse aggregates only adopt stone with
particle size from 20 to 40 mm and remove small stones with particle size from 5 to
20 mm, increasing the sand ratio; the effect of ideal lowest void content as well as
higher strength can be realized without adding cement content.
The above three theories regarding mix design have consisted the basis on which
we make any mix proportions so far.
SSA method regards how to decrease the total surface face as core, while
maximum density and gap grading methods regard how to boosting unit weight of
aggregate and minimum void content as their cores, respectively. It seems that the
former and latter theory were contradictory, But after careful analysis, you may nd

that maximum density and gap grading method are supplements to SSA method.
SSA method is a method with the longest using history and greatest impact. The
Chinese mix design speci

cation for normal concrete has continuously adopted this
method as theoretical basis, so it is the same in foreign countries. SSA method has
been applied commonly within fields of highway and civil airport construction in

the near 20 years. The older engineers utilize SSA more frequently than the younger
engineers in the same working unit. As for mix proportion of equal strength grade
in the same construction site, aggregate consumption

xed by the two methods

varies a lot. Table 1.1 re ects the mix proportions of stiff concrete with designed

flexural strength of 5 Mpa done by older and younger engineers at Baiyun Airport