Sustainable Concretes for Structural Applications
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The specimens were molded with different dimensions that matched the requirements
of their standard tests. The samples were covered with a wet plastic sheet to prevent
them from dripping water in the first 24 h of curing. Then, the concrete specimens
were demolded and immersed in lime-saturated water at 23 °C until reaching their
testing ages. For each test, three samples were prepared, and the average value is
reported as the final result.
2.3 Testing Methods
Compressive and splitting tensile strength tests were performed using a 3000-KN
universal compression machine in accordance with ASTM C39 (2003) and ASTM
C496 (2011), respectively. Cubic specimens 100 mm in size were used to determine
the compressive strength, whereas cylindrical specimens with a diameter of 100 mm
and a height of 200 mm were used to evaluate the splitting tensile strength of the
concrete. The flexural strength tests were carried out as per EN 14651 (2007) on
prismatic beams with dimensions of 150 × 150 × 600 mm. The modulus of elasticity
tests was conducted on the cylindrical specimens with dimensions of 100 × 200 mm
as per ASTM C469 (2014). To study the microstructure of concrete made with
different types of binders, several images were taken from the fracture surface of
concrete specimens by using scanning electron microscopy (SEM) method.
3 Results and Discussion
3.1 Consistency
The consistency of the different mixes developed in this study was evaluated by a
slump test, and the results are shown in Table 1. The slump values of the concrete
varied between 19 and 23 cm.
A minimum of 1% superplasticizer was required to adjust the consistency of
concrete. Higher content of superplasticizer was used in CSA-based and in blended
concretes compared to that of OPC to obtain an almost similar slump value. This
can be explained by the fineness of CSA and a GBBS particle size that is lower
compared to that of OPC. Furthermore, the fast rate of CSA cement hydration and
its high demand of water to generate ettringite are other reasons that necessitate
the addition of greater amounts of superplasticizer. The results further indicate that
the incorporation of steel fibers had a negative influence on the properties of fresh
concrete. The long steel fibers and aggregates interlock in the body of concrete and
lead to a reduction in the slump value. To attain the same consistency in the concretes
with and without fibers, the content of the superplasticizer was slightly increased.
253
The specimens were molded with different dimensions that matched the requirements
of their standard tests. The samples were covered with a wet plastic sheet to prevent
them from dripping water in the first 24 h of curing. Then, the concrete specimens
were demolded and immersed in lime-saturated water at 23 °C until reaching their
testing ages. For each test, three samples were prepared, and the average value is
reported as the final result.
2.3 Testing Methods
Compressive and splitting tensile strength tests were performed using a 3000-KN
universal compression machine in accordance with ASTM C39 (2003) and ASTM
C496 (2011), respectively. Cubic specimens 100 mm in size were used to determine
the compressive strength, whereas cylindrical specimens with a diameter of 100 mm
and a height of 200 mm were used to evaluate the splitting tensile strength of the
concrete. The flexural strength tests were carried out as per EN 14651 (2007) on
prismatic beams with dimensions of 150 × 150 × 600 mm. The modulus of elasticity
tests was conducted on the cylindrical specimens with dimensions of 100 × 200 mm
as per ASTM C469 (2014). To study the microstructure of concrete made with
different types of binders, several images were taken from the fracture surface of
concrete specimens by using scanning electron microscopy (SEM) method.
3 Results and Discussion
3.1 Consistency
The consistency of the different mixes developed in this study was evaluated by a
slump test, and the results are shown in Table 1. The slump values of the concrete
varied between 19 and 23 cm.
A minimum of 1% superplasticizer was required to adjust the consistency of
concrete. Higher content of superplasticizer was used in CSA-based and in blended
concretes compared to that of OPC to obtain an almost similar slump value. This
can be explained by the fineness of CSA and a GBBS particle size that is lower
compared to that of OPC. Furthermore, the fast rate of CSA cement hydration and
its high demand of water to generate ettringite are other reasons that necessitate
the addition of greater amounts of superplasticizer. The results further indicate that
the incorporation of steel fibers had a negative influence on the properties of fresh
concrete. The long steel fibers and aggregates interlock in the body of concrete and
lead to a reduction in the slump value. To attain the same consistency in the concretes
with and without fibers, the content of the superplasticizer was slightly increased.