AbstractThe escalating manufacturing cost of ordinary Portland cement has led to the search for less energy intensive materials. One such material is condensed silica fume (CSF) which is an industrial by-product and until recently was discarded as waste. Research has shown that the addition of CSF to concrete can have the dual benefits of increased strength and improved durability.
In the present study experimental and numerical techniques were employed to investigate the mechanical and fracture characteristics of CSF concrete wet cured at 20° C and 50° C.
Whereas the high temperature curing resulted in increased compressive strength at early age, the specimens cured at 20° C exhibited higher strengths beyond 28 days. It was also found that increasing the CSF content did not significantly increase the tensile strength and, in fact, as with the compressive strength, a small decrease was obtained when the CSF content was increased from 16% to 20%. Furthermore, curing temperature did not appear to have a major influence on the tensile strength, nor did it affect the relationship between the static modulus of elasticity E and the compressive strength. However, a reduction in E was obtained for compressive strengths beyond 90 N/mm2.
Several geometries, namely the Compact Compression Specimen (CCS) and the Singly and Doubly Notched Axial Splitting Specimens (SNASS and DNASS), were employed in the fracture studies. Detailed finite element analyses for these geometries were carried out using triangular and rectangular isoparametric elements. The results for the stress distributions demonstrated the existence of large tensile stresses at the root of the notch, thus confirming that failure is of the opening (mode 1) type.
In evaluating the fracture toughness, both the stress intensity factor and the energy approaches were used. As no allowance was made for the tortuosity of the fracture surface, the former approach was considered to be more reliable in the present work. This was subsequently used to assess the degree of brittleness of the concrete. It was found that beyond a compressive strength of about 90 N/mm2, increased brittleness was obtained with increasing strength.
Some of the fracture tests were conducted on concrete reinforced with polypropylene fibres. The post cracking performance of such concrete was assessed using a toughness index evaluated from the area under the load-displacement relationships.
|Date of Award||1992|