Research On Pozzolanic Activity Of Volcanic Rocks In Cement-based Materials And Its Application

With the rapid development of civil engineering industry in China,the production demand of cement and concrete has increased in recent years,which not only causes the consumption of a large amount of non-renewable resources,but also makes the greenhouse effect and global warming more serious,bringing great adverse effects on human survival and development.Therefore,research and development of mineral admixtures have been rasing so that can replace the cement,thereby reducing the consumption of non-renewable energy and promoting the healthy and sustainable development of cement and concrete industry.Volcanic rock is rapidly cooling products of magma erupting to the surface.The volcanic rock is abundant in reserves and widely distributed in China.A large number of experiments and studies have shown that they have vitreous structure and are rich in SiO₂ and Al₂O₃ so they have pozzolanic activity.When cement and concrete are mixed with the volcanic rock powder,the activity components SiO₂ and Al₂O₃ are respectively hydrated with calcium-hydroxide and high alkaline calcium-silicate-hydrates produced from cement clinker to form low alkaline calcium-silicate-hydrates and calcium-aluminate-hydrates,which is secondary hydration?pozzolan effect?.Therefore,volcanic rock is a mineral admixture that can partially replace cement in cement-based materials.In order to explore the feasibility of volcanic rock used as supplementary cementitious material in cement-based materials,and some volcanic rocks were collected and selected in Northeast China,and pozzolanic activity of the volcanic rocks in the cement-based materials was respectively researched by using the pozzolanic activity component calculated by results of chemical composition analysis and XRD method,pozzolanic activity index obtained by mortar strength ratio and the specific strength indicators obtained by specific strength analysis method.The correlation between the pozzolanic activity component and the SiO₂ content,and relationship of pozzolanic activity component with pozzolanic activity index was analyzed,and then influences of mixing amount of volcanic rock,curing time and water-to-binder ratio on the contribution rate of pozzolanic effect were discussed.The results on pozzolanic activity of volcanic rock evaluated by the pozzolanic activity component shows that the pozzolanic activity of volcanic rocks WY and CN₁ are relatively higher,while the pozzolanic activity of volcanic rocks JP,AL₁ and AL₂ are lower.The correlation between the pozzolanic activity component of volcanic rocks and the SiO₂ content of volcanic rocks is positively fair,and their correlation coefficient R=0.93 shows that the pozzolanic activity component of volcanic rock is closely related with SiO₂ content of volcanic rocks,that is,the larger SiO₂ content,the larger the pozzolanic activity component,which is suitable for supplementary cementitious materials in the cement-based materials.The compressive strength and pozzolanic activity index of cement mortar mixed with volcanic rocks were used to evaluate the pozzolanic activity of volcanic rocks.The results indicated that all of the volcanic rocks can be used as natural pozzolanic materials for cement mortar and concrete,and then the pozzolanic activity of volcanic rock WY is the largest,and the pozzolanic activity of volcanic rocks JP and AL₁ is smaller.The pozzolanic activity index of volcanic rocks is positively correlated with the pozzolanic activity component in cement-based materials.The fitted linear regression equation reveals accurately the correlation between them.The fitting linear equation might be applied to convert the pozzolan activity index to the pozzolanic activity component.Pozzolanic activity of volcanic rocks was assessed by means of specific strength indicators in the volcanic rock/cement mortar,and the influences of mixing content,curing time and water-to-binder ratio on pozzolanic effects of volcanic rock.That is found that the pozzolanic activity of volcanic rock WY is the largest,and the pozzolanic activity of volcanic rocks JP and AL₁ is smaller.The contribution rate of pozzolanic effect volcanic rock increases with increasing content of volcanic rock and decreases with increasing water-binder ratio in the mortar.Prolonging curing time is beneficial to pozzolanic effect of volcanic rocks.Pozzolanic activity of volcanic rocks was evaluated on specific strength indicator in the concrete mixed with volcanic rock,and the influences of mixing content and curing time on pozzolanic effects of volcanic rock.It is known that pozzolanic activity of volcanic rock CN₁is the largest,and the pozzolanic activity of volcanic rocks AL₂ is smallest.Increasing content of volcanic rock is beneficial to pozzolanic effect of volcanic rocks.