| Stone relics are among the most important parts of Chinese cultural relics.Since most of them are exposed to the outdoor environment,they have to be confronted with corrosion,weathering,cracking,breaking and/or fractures.Cementious materials are so far the commonly-used materials to repair the diseased stones.However,they are not able to provide suitable compatibility and high strength simultaneously.We herein developed a series of geopolymers as reparing materials for the protection of stone relics,providing both good compatibility and high strength.Xanthan gum-and polystyrene emulsion-modified geopolymers were prepared and studied,based on which innovative breathable repairing materials were developed and applied in the project of Guangzhou Museum.In the first part of our work,xanthan gum(XG)-modified geopolymers were prepared and it is found that the introduction of XG is indeed able to improve the mechanical properties of the geopolymers effectively.The mechanical properties of the XG-modified geopolymer achieves the highest level with a flexural strength at about 8.2 MPa when dosage of XG is 0.6 wt%.The value is 36% higher than that of the geopolymer without adding XG.Additionaly,XG exhibits obvious thickening effect on the fresh geopolymer paste,by which both the plastic viscosity and yield stress improved.XG could also accelerate the setting of geopolymers and show water retention ability.The addition of XG destroys the flocculation of metakaolin therefore it is able to disperse homogeneously in the formed geopolymer pastes.Polystyrene(PS)latex was synthesized by surfactant-free emulsion copolymerization of styrene and sodium styrene sulfonate(NaSS).The particle size of the obtained PS emulsion can be controlled by the amount of NaSS.The effect of latex amount and latex particle size on the mechanical strength of the formed geopolymers was studied and it is observed that the addition of PS latex has no positive effect on the compressive strength of geopolymers.However,the bending strength of geopolymer can be improved over 16% when certain amount of latex particles(0.63 wt% of metakaolin)was added.When the particle size is in the range of 40-200 nm,the compressive strength and flexural strength of geopolyme increased with the increase of particle size.To meet the requirements of permeability,which is necessary for repair material used in the application of stone cultural relics protection,air-entraining agents were added into the polymer modified geopolymer.Three types of air-entraining agent were added into xanthan gum modified geopolymer,including sodium abietate,Lg-2588 and Y-1.Results show that Y-1 has the bset performance,which could improve the porosity of geopolymer from 29% to 56%.When the dosage of Y-1 is 0.1 wt%,the porous geopolymer has most comprehensive performance.The addition of Y-1 introduced a large number of bubbles into the XG modified geopolymer.SEM graphs show that the average size of bubbles is about 100 ?m.Therefore,we chose Y-1 as the air-entraining agent and prepared a novel geopolymer repair material.The compressive strength and bonding strength of this geopolymer repair material could reach to 58 MPa and 2 MPa respectively.Freeze-thawing,acid-resisting and stability tests reveal that the geopolymer repair material could meet the standards in application.This material was applied in the field tests at Guangzhou Museum and results show that geopolymer repair material is an ideal adhesive and surface repair material. |
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