Abstract:
The aim of this study was to evaluate the performance of high strength
concretes (HSC) containing supplementary cementitious materials. Now a
days concrete had demanding requirements both in terms technical
performance and economy. The main aim of the investigation program is
first to prepare the strength of concrete of grade M80 with locally available
ingredients and then to study the effects of different proportions of silica
fume and silica fume in conjunction with fly ash in the mix and to find
optimum range of silica fume and fly ash content in the mix. The silica fume
and fly ash is added by weight of cement as a replacement. The concrete
specimens were tested at different age levels,7-days and 28-days for
mechanical properties of concrete, namely, cube compressive strength, and
length change due to drying shrinkage tests also fresh concrete properties,
using slump test has been made.
This research presents a part of an ongoing experimental laboratory
investigation being carried out for production and characterization of high
strength concrete (HSC) for heightening of an existing concrete dam in the
south of Sudan, brief description of the main features of the dam and
concrete works is presented. Hundreds of specimens were performed and
tested using local Sudanese aggregates with addition of supplementary
cementitious materials (Silica Fume and Fly Ash) and super plasticizers.
Various percentages of silica fume (SF) and fly ash (FA) were added at
different water/cementitious materials ratios (w/cm). Thirty three trial mix
design of grade (80 MPa) HSC had been success fully produced and their
mechanical properties were measured and documented. Two approaches
were used in the study statistical approach which described in ACI 211.4 and
another one is use JMP statistical program to make a modeling for predicting
Compressive Strength and Slump for HSC.
The results have offered an important insight for optimizing the
rheological characteristics of HSC and permitted to develop guidelines for
optimum mix design methods for HSC from locally available aggregates in
Sudan. Optimum w/cm ratio it ranges from 0.19 to 0.3. Optimum
replacement percentage of SF is not a constant one but depends on the w/cm
ratio of the mix it ranges between7 to 15% of cementitious materials. SF
contributed to both short and long-term properties of concrete. It is
concluded that local concrete materials, in combination with supplementary
cementitious materials can be utilized in producing high strength concrete in
Sudan