15-11-2012, 06:13 PM
DEVELOPMENT OF LOW SHRINKAGE HIGH PERFORMANCE CONCRETE WITH IMPROVED DURABILITY
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ABSTRACT
The main goal of this study is to develop
Low-shrinkage for high-performance concrete
To reduce early age cracking
Reduce reinforce-ment corrosion
To provide long service to concrete structures.
This paper presents a summary of the results related to the evaluation for
mechanical, and durability properties of different HPC with a w/c ratio of 0.35.
In this study IC or SRA is used meet all performance requirements in terms
Workability
hydration characteristics
volume stability
strength and durability under severe exposure conditions
INTRODUCTION
To that effect, three concrete technologies are being investigated, namely:
Supplementary cementing materials, i.e. silica fume (SF) and slag, to reduce concrete permea-bility and partially replace the cement used in concrete
Internal curing (IC) with pre-soaked LWA sand to provide enhanced concrete curing and reduce early age shrinkage cracking and
SRA to reduce drying shrinkage cracking
EXPERIMENTAL PROGRAM
MATERIALS
For an objective comparison of the above technologies, different HPC formulations were developed and based on the same basic proportions, such as:
(i) water-cement ratio of 0.35
(ii) cement/sand/stone mass ratio of 1:2:2 and
(iii) maximum aggregate size of 10 mm.
AMOUNT OF HYDRATION PRODUCTS
Thermo-gravimetric analyses of finely crushed mortar specimens were conducted to characterize the hydration process and major products of hydration, including contents of absorbed water, and calcium silicate hydrate (C-S-H), which is the main compound in hardening cement responsible for strength increase.
Mechanical Properties
The compressive strength was measured on 100x200 mm concrete cylinders at 7 days, 28 days, 56 days and 90 days after casting.
Figure 3 shows the development of compressive strength over time for the different concretes.
Short-term shrinkage and long-term drying
The free shrinkage of sealed concrete specimens was determined by measuring the total strain and subtracting the thermal strain obtained from measurements of temperature and thermal expansion coefficient.
Figure 4 presents the average shrinkage strain measured on a set of three 75x75x300 mm prismatic specimens over a period of 28 days.
It is shown that the free shrinkage strain of HPC-6 is quite high and is most likely large enough to produce cracking if shrinkage had been fully restrained in these specimens.