No abstract

Ambient-cured heavyweight geopolymer concrete (HWGC) is a new type of concrete that combines the benefits of both heavyweight concrete (HWC) and geopolymer concrete (GC). HWGC provides proper protection from the sources that emit harmful radiations in medical and nuclear industries. Furthermore, HWGC may also be used in offshore structures for pipeline ballasting and similar underwater structures. In this study, heavyweight aggregates (magnetite) have been used and replaced by normal-weight coarse aggregates in GC at volume ratios of 50, 75, and 100% to attain heavyweight classification according to British standards. This study investigates the impacts of high temperatures on standard ambient-cured geopolymer concrete and ambient-cured HWGC through its residual properties regarding compressive and tensile strengths, mass loss, spalling intensity, and flexural strength. The residual properties were examined by heating 100 × 200 mm cylinder specimens to 100, 300, 600, and 900 °C. The results indicated that the maximum compressive strengths of 40.1 and 39.0 MPa were achieved by HWGC at 300 and 100 °C, respectively. The overall result shows that the strength of HWGC increases by increasing magnetite aggregate proportion, while the mass loss, intensity of spalling, and loss of strengths is proportional to temperature after a certain point. Minor spalling with holes and cracking was observed only at 900 °C in HWGC.

Heavyweight self-compacting concrete (HWSCC) and heavyweight geopolymer concrete (HWGC) are new types of concrete that integrate the advantages of heavyweight concrete (HWC) with self-compacting concrete (SCC) and geopolymer concrete (GC), respectively. The replacement of natural coarse aggregates with magnetite aggregates in control SCC and control GC at volume ratios of 50%, 75%, and 100% was considered in this study to obtain heavyweight concrete classifications, according to British standards, which provide proper protection from sources that emit harmful radiations in medical and nuclear industries and may also be used in many offshore structures. The main aim of this study is to examine the fresh and mechanical properties of both types of mixes. The experimental program investigates the fresh properties of HWSCC and HWGC through the slump flow test. However, J-ring tests were only conducted for HWSCC mixes to ensure the flow requirements in order to achieve self-compacting properties. Moreover, the mechanical properties of both type of mixes were investigated after 7 and 28 days curing at an ambient temperature. The standard 100 × 200 mm cylinders were subjected to compressive and tensile tests. Furthermore, the flexural strength were examined by testing 450 × 100 × 100 mm prisms under four-point loading. The flexural load-displacement relationship for all mixes were also investigated. The results indicated that the maximum compressive strength of 53.54 MPa was achieved by using the control SCC mix after 28 days. However, in HWGC mixes, the maximum compressive strength of 31.31 MPa was achieved by 25% magnetite replacement samples. The overall result shows the strength of HWSCC decreases by increasing magnetite aggregate proportions, while, in HWGC mixes, the compressive strength increased with 50% magnetite replacement followed by a decrease in strength by 75% and 100% magnetite replacements. The maximum densities of 2901 and 2896 kg/m3 were obtained by 100% magnetite replacements in HWSCC and HWGC, respectively.