Reseach On The Swelling Inhibition Mechanism And Modification Experiment Of Pisha Sanstone Montmorillonite

Pisha sandstone is an underdevelopment mudstone, sandstone which is located in an adjacent region close to Inner Mongolia Autonnmous Region, Shanxi and Shaanxi province, it is hard when it is dry but would collapse when immersed in water. Due to PS’s unsatisfactory bonded mechanism, soil erosion occurs frequently, soil and water loss has become the main environmental disaster to local agricultural production and environment, and the local people named it "Pisha sandstone" due to its harm such as arsenic. In this paper, the Pisha sandstone was trated as a valuble resource from a new point of view, and a new construction material with low CO₂ production, economy and a reliable strength. The Pisha sandstone was reused to treat the soil and water loss of Pisha sandstone area and the technology of modified Pisha sandstone were established. The main work of this paper as follow:The formation, distribution, composition of chemistry and mineral of Pisha sandstone were studied, the mineral of Pisha sandstone was divided into three categories, coarse particle, cementing material and expansion material. The saturated water absorption, feacture of collapse in water, collapse resistance and swelling volume of Pisha sandstone were analysis by experamental. The values of CIA, saturated water absorption, collapse resistance and free swelling ratio are 56.8～67.6,42%～51%,2.7% and 43%, respectively, and the feacture of collapse in water could be classified into type I. Pisha sandstone was a kind of sandstone with low collapse resistance and strong swelling. The results of white and red Pisha sandstone showed that the montmorillonite was attributed to Ca-montmorillonite, it was the product of feldspar weathering and it also was the main cause of Pisha sandstone collapse in water. The value of methylene blue adsorbed, swelling volume, CEC, and molecular structural of white and red montmorillonite were 32.72g/100g and 28.21 g/100g,5.1mL/g and 5.0mL/g, 112.7mmol/100g and 104.9mmol/100g, Ca_0.43Mg_0.23Na₍0.150K_0.04(Si_7.69Al_0.31)(Al_2.64Fe_0.48Mg_0.71) O₂₀（OH）₄ and Ca_0.61Mg_0.22Na_0.09K_0.05(Si_7.11Al₉0.89))(Al_2.04Fe_1.070Mg0.90 O₍200（OH）₄, respectively. The swelling inhibition mechanism and modification experiment of Pisha sanstone montmorillonite, the capacitor model, secondary replacement concept, and sequence of cation exchange were established. It showed that the ion valence, ion radius and charge density of ion have a remarkable influence on the inhibition of volume swelling, and the swelling volume decreased with the charge density increased. In the +1,+2 and +3 chlorine salts solution, the swelling volume of montmorillonite are 3.31 mL/g,2.6 mL/g, and 2.5 mL/g, respectively. The value of Zeta potential increased from -18mV to 5.0mV when the charge density increased from 0.10C/m² to 0.18C/m². The decreased of the absorption peaks at 3624cm^-1,912 cm^-1 and 3410cm^-1,1032cm^-1,512cm^-1,425cm^-1 was ascribed to Mg²⁺, Fe²⁺ substituted Al³⁺ and Al³⁺ substituted Si⁴⁺, respectively.The experimental were used to evaluate the effect of alkaline concentration, curing temperature and curing age on the crossion of montmorillonite. The result show that the dissolution rate of Si⁴⁺, Al³⁺,Ca²⁺ were 3.91%,5.56% and 4.13% when curing at 25℃, and it was 19.8%,12.7% and 1.23% while curing at 80℃. A higher curing temperature could improve the efficiency alkaline crossion. The absorption capacity of alkaline by montmorillonite were 52.7mg/g,53mg/g and 61mg/g when the NaOH concentration were 0.1mol/L,0.5mol/L and 1.0mol/L, respectively. The XRD, TG/DTG and SEM-EDS results showed that the product of alkaline corrosion montmorillonite were C-S-H and zeolite. The alkaline corrosion of montmorillonite has three types, type I （NaOH<0.05mol/L）, alkaline absorption, type Ⅱ （0.05mol/L<NaOH<0.1 mol/L）, ion exchange and substitution, type Ⅲ （0.5mol/L<NaOH 25℃,0.1mol/L<NaOH 80℃）, alkaline corrosion. And the process of alkaline corrosion of montmorillonite has four stages, a. alkaline absorption, b. ion exchange and substitution, c. alkaline corrosion acceleration, d. scale formation and precipitation.The modified Pisha sandstone material was produced by using the ion exchange and alkaline coreosion technologies. The results showed that the dosage of NaOH and fly ash, curing age and curing temperature had signification influence on the strength of Pisha sandstone based mortars. The dry and water-saturated compressive strength of Pisha sandstone mortars were 11.6 MPa and 8.7 MPa, respectively, and the Pisha sandstone-fly ash samples were 20.3 MPa and 17.6 MPa, respectively. The modified Pisha sandstone material has preferable water resistance, the softening coefficient and water permeability were 0.65～0.95 and 5.1×10-6cm/s, respectively. The results of XRD, FTIR, TG-DTG and SEM-EDS showed that the main products of Pisha sandstone based mortars were alkali geopolymer gels, C-A-S-H gels, analogous zeolites, and the calcite which was the carbonization products of C-S-H gels. The results of resistence of acids and alkali solution corrosion tests were showed that Pisha sandstone based mortars has preferable properties of resistence in water, Na₂SO₄ and CaCl₂ soultions, however, the resistence of Pisha sandstone based mortars in HC1 solution is low.