Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Splitting tensile strength

Using Citric Acid As An Admixture and It's Influence on Some Properties of Concrete

Wasan I. Khalil

Engineering and Technology Journal, 2009, Volume 27, Issue 1, Pages 32-41

The objective of this investigation is to find the effectiveness of the citric acid as
retarding admixture. The experimental results indicate that the optimum dosage of citric
acid is 0.02% by weight of cement. This dosage causes a delay in initial and final setting
time of 1:42 and 3:18 hour: minute, respectively; and a reduction in water-cement ratio
of 13% relative to reference concrete mix. So, citric acid can be classified according to
ASTM-C494 as water-reducing and retarding chemical admixture type D.
The investigation also extends to evaluate the effect of using citric acid on
properties of concrete such as, compressive strength, splitting tensile strength, modulus
of rupture and dynamic modulus of elasticity at normal conditions and after exposure to
salt solutions. Generally the results indicate that using citric acid in concrete enhance it's
properties at normal conditions, the percentage increase in compressive strength,
splitting tensile strength, modulus of rupture and dynamic modulus of elasticity at age
180 days was about 56%, 13%, 24% and 8% respectively relative to reference concrete.
Also it was observed that concrete containing citric acid has good performance after 180
days exposure to salt solution in comparison with reference concrete.

Effect of Coarse Aggregate Characteristics on Drying Shrinkage of Concrete

Tareq Salih Al-Attar

Engineering and Technology Journal, 2008, Volume 26, Issue 2, Pages 146-153

Concrete is a composite material, consisting, mainly, of three phases: coarse
aggregate, cement mortar, and the interface zone between them. The characteristics
of the interface zone largely govern the bond between cement paste or mortar and
aggregate. The restraining effect of aggregate to drying shrinkage strain depends
much on the bond between aggregate and cement paste.
In this paper, it is aimed to investigate the effect of coarse aggregate
characteristics, that affect bond strength, such as; type, shape, surface texture, and
moisture content, on drying shrinkage. Four types of coarse aggregate were used.
Three of them were normal-weight, while the fourth was a light-weight one. Each
type of coarse aggregate was used in two moisture conditions, dry and saturated.
The testing program extended to 150-days age and comprised; length change,
modulus of elasticity, compressive and splitting tensile strength of concrete.
It is concluded that using saturated coarse aggregate always yields higher
shrinkage strain than dry aggregate. The percentage increase seems to be affected
by the aggregate water absorption. At early ages, After 28 days, there is large
differences in relative shrinkage for different mixes. Later than 28 days, the
variation in ratios settled to approximately fixed values