| dc.description.abstract | A research programme to investigate the detrimental
effects of'sulphate, chloride, fluoride and phosphate
of effluent origin on concrete was conducted. The
irrq::ortanceof these effects is increasing because most of
the sewer fabrics through which both domestic and in-
dustrial effluents flow, are made of concrete. Since the
effects of these ions lead to corrosion of concrete, one
of the objectives was to provide information as to which
of the four cement types used, was best for each of the
aggressive environments.
The research programme included four cement types,
namely, Ordinary Portland Cement, Sulphate-Resistant
Portland Cement, Moderate Type II Cement and Pozzolanic
Cement, whose Compositi®ns are 9iven in table 4-1. Two
sizes of cubes, 13.0 mm and 70.7 mm were made out of each
cement type. The 70.7 mm cubes were prepared using r\T/c
ratio of 1:3 and 13.0 mm cubes were of Hlc of 1:5 bv usin(
stabilised cement paste (Sec. 3.5.1. and, 3.5.2.
The 13.0 mm cubes were immersed in sulphate. chloride,
fluoride and phosphate solutions, of different concentrations,
after curing in water for a period of twenty eight
days. Compressive strengths were measured for cubes after
every 28 days, ie. after hydration in water, 28 days after
immersing in ionic solutions, 56 and 84 days respectively.
The 70. 7 mm cubes we re submerged in ionic sol u--
tions of the same conc ent.r at.Lons as f or the small
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cubes, for a period of six months.
Since the solu-
tions were acidic, their pH was adjusted weekly to
make sure that the pH was constant throughout the peri-
od of investigation. At the same time the mass and
length changes were taken on a weekly basis.
Before each pH adjustment, some solution was sam-
pled from the bulk of the solution for ionic analysis.
This enabled us to estimate the amount of each of the
ions used up for chemical reaction with the cement and
hence the effect of the ion as measured by the mass
and volume changes.
During the period of the investigation
both the pH and volume of the solution was kept
as constant as possible.
The 70.7 mm cubes were crushed after six months for
compressive strength measurements. The compressive
"." .
strengths measurement was another yardstick to measure
the effect of the various ions on the cement cubes.
Portions of the 70.7 mm crushed cubes were sampled
for ionic penetration measurements.
It was found that
most of the ions were found on the surface and very few
at the centre of the cubes.
A comparison of mass and volume changes, compresive
strengths, ionic analyses and ion penetration
measurements, showed that the four rypes of ccrrrrent.s responded
differently to the -four types of ions investigated.
It was found that under sulphate environment the sul-
phate-resistant Portland ce~ent could be used while in
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chloride and fluoride environments, type II would be
recommended as the best. Pozzolanic cement can be used
for environment with low sulphate, interchangeably with
type II cement. The phosphate does not have deleterious
effect on the four cement types used, and infact it has
the advantage of increasing' compressive strength and
resistance to corrosion. However, under moving water
conditions we could not predict the fate of the crys-
tals formed from the phosphate cement reaction. | en |
