Suppressing Measures Against Alkali-silica Reaction In The Dam Concrete For The Jinping-Ⅰ Hydroelectric Project

In the thesis, some questions are studied about suppressing the alkali-silica reaction (ASR) of the sandstone aggregate to be used in the dam concrete for the Jinping-â… Hydroelectric Project. The conculsions are summarized as follows:(1) Sandstone aggregate and sandstone-marble combination aggregate are alkali-silica reactive and indicative of potentially deleterious expansion, no "passimum" phenomenon was observed.(2) There was no difference between Classâ… and Classâ…¡fly ash on suppressing ASR. All the 9 fly ashes from Jinping-â… Hydroelectric Project could effectively suppress ASR of sandstone at 30% replacement level, including Pingliang Classâ… and Classâ…¡fly ash with CaO content about 8%. Considering the difference between dam concrete and normal concrete and the variation of the reactivity of sandstone, the safe replacement level of fly ash is suggested to be no less than 35%.(3) There is no remarkable relationship between any chemical composition of fly ash and the suppressing effect on ASR. As the criteria for selecting proper fly ash source, the chemical index C_FA is more reasonable than the CaO content or alkali content. The formula of C_FA is:If C_FA is below 0.40, the fly ash at 30% replacement level can effectively inhibit the ASR of sandstone used in the Jinping-â… Hydroelectric Project, and if C_FA is above 0.40, more fly ash would be needed.At 30% replacement level, there is no remarkable relationship between mineralogical composition of fly ash and the suppressing effect on ASR. Replacing the SiO₂ and Al₂O₃ content in C_FA by amorphous SiO₂ and amorphous Al₂O₃ content didn't increase the relativity.The fineness of fly ash influences the suppressing effect on ASR, but not as obviously as C_FA. The physical-chemical index C made up of C_FA and specific surface area can reflect the influence of physical and chemical quantities of fly ash on suppressing effect on ASR. The formula of C_FA is:(4) Fly ash would be terriblely activated in 80℃, 1mol/L NaOH and saturated Ca(OH)₂ solutions so that the suppressing effect on ASR tested by AMBT was much better than the effect tested by ACPT.Most compositions of fly ash could dissolved except mullite which makes up about 20% of total fly ash by weight, this phenomenon can explain why the influence of chemical compositions is bigger than that of mineralogical compositions.The main productions of fly ash in hot alkaline solution are P zeolite and C-S-H gel. P zeolite is beneficial to suppressing ASR. C-S-H gel can improve the strength of mortar, but no influence on ASR.(5) If reactive aggregate is used in dam concrete, the reactive stone powder brought in with fine aggregate and the air bubbles entrained by AEA will reduce ASR expansion greatly. The overall effect of these self-immunity mechanisms of dam concrete is the reduction of ASR expansion by 40% to 80%. So ASR expansion in real dam concrete structures is not as serious as observed in standard tests.(6) Ground lithium slag can efficiently suppress ASR, but it will cause early expansion of mortar or concrete, this expansion should be separated when testing the suppressing effect. Composite powder can effectively inhibit the expansion due to ASR at 30% or more replacement level. HLC-ASW type superplasticizer can reduce about 20% of expansion due to ASR, which is much better than normal naphthalene type superplasticizers.