| Lithium slag is a waste residue that comes from the process of production of lithium carbonate by spodumene ore as raw material. Now, some lithium slag as mixed materials or admixtures is used in cement or concrete, but its utilization is low. In order to use a large amount of lithium slag and reduce the cost of concrete, the paper studies hydration characteristics of lithium slag composite binding material and its role in the concrete hardening process, the conclusion follows:(1) The chemically combined water of lithium slag composite binder is less than 8%, and the reaction extent of lithium slag is less than 3% when the age is 1day in standard curing, but all increases with the extension of age. The chemically combined water of lithium slag composite binder and the reaction extent of lithium slag at high temperature curing(50℃ and 100℃) or alkali stimulate(pH=13.5 NaOH solution for mixing water)or two composite curing are 1~5 times than standard curing. In contrast, the effect order of four kinds curing method for chemically combined water of lithium slag composite binder and the reaction extent of lithium slag is composite curing> alkali stimulate>high temperature> standard curing.(2) The relative error is less than 4% about the results of hydration product volume fraction of Powers and this paper presents a calculation method when admixtures is 0%, which indicating the calculation methods in the paper is reliability. It is found by SPSS that the volume fraction of unhydrated particles,pores and CSH are affected by water-cement ratio×content×admixture species(60.33%), water-cement ratio×admixture species(91.79%) and water-cement ratio(89.23%), the volume fraction of CH and aluminate phase are affected by content, the values are 6.17% and 16.65%, respectively.(3) The spectral characteristics peak of CH, CSH and AFt is strong after lithium slag replace cement.The spectral characteristics peak of CH becomes weak when the content of lithium slag increase or the water-cement ratio decrease, but the characteristic peaks of CSH adsorbed water enhanced. Chemical shrinkage of cement-lithium slag slurry increases with curing period prolonged, and the correlation coefficient was 0.98 or more after hyperbolic model, but the value of hydration coefficient k in hyperbolic model were selected that based on water-cement ratio, content and admixture species.(4) The calculation method of hydration products content containing admixtures was proposed that based on the calculation method of pure cement hydration products content, the results found that, thehydration products CH and CSH content of composite binder has been reduced due to the incorporation of lithium slag, but he total porosity is opposite trend. Late(28d) compressive strength of cement-lithium slag mortar is higher 0.4~4.2% than pure cement mortar when dosage of lithium slag is 20%. Compared with cement-fly ash mortar, the total porosity and content of CH of cement-lithium slag mortar is smaller compared with fly ash and steel slag, CSH content and compressive strength of cement-lithium slag mortar are greater than cement-fly ash mortar.(5) It is remarkable that the influence of lithium slag content and curing age on compressive strength and chlorine ion penetration. When the content is 20%, the chlorine ion penetration of lithium slag concrete is equal or higher and the strength class of 28 days is C55 that is higher than pure cement concrete(C50).The strength grade of lithium slag concrete is equal with pure cement concrete, but compressive strength of the former is higher than the latter in the remaining content and water-cement ratio. The compressive strength of alkali-lithium slag concrete is higher than pure cement concrete, but their strength level is same when the content of lithium slag is within 40%, the content of lithium slag is increased 1 times, which indicate the effect of alkali stimulate to lithium slag concrete is good.(6) Lithium slag has a certain activity, it’s content increases from 0% to 60%, activity factor is first increased and then decreased. When the content is 20% to 30%, physical and chemical effects of lithium slag reach to the maximum, and the activity factor R is 1 or more. Hydration 1d, lithium slag particle surface is wrapped in a layer of hydration products and it is gradually increasing with the curing period prolonged, which explained lithium slag particles have been involved in second hydration.(7) The hydration products of cement-lithium slag slurry is CH, CSH gel and unhydrated particles and a small amount of AFt after lithium slag as mortar fine aggregate, and the hydration products CH increases linearly with the increase of the replacement rate of lithium slag. When the replacement rate of lithium slag is 70% and curing period is 28 d, the flexural/compressive strength of cement-lithium slag are higher56.35% and 64.68% than pure cement mortar, and it is higher than cement-fly ash mortar at the same replacement rate. The peak stress of cement-lithium slag mortar is about 1.39, 1.73 and 1.23 times of pure cement mortar; and the external loads acting of the former is about 1.33, 1.68 and 2.44 times of the latter. |
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