Nanoscale modifier as an adhesive for hollow microspheres to increase the strength of high-strength lightweight concrete

摘要

The paper presents the results of a study of the physical-mechanical and operational properties of high-strength lightweight concrete and the influence of nanoscale modifier on these properties. The nano-modifier and its method of application to improve the properties of lightweight concrete with hollow microspheres at 10-25% are proposed. The method to control structure formation processes by the nano-modification is shown. The nanoscale modifier is grafted onto the surface of the hollow filler and interacts with cement and its hydration products (calcium hydroxide). This local activation of the hydration of Portland cement and the formation of an additional amount of calcium hydrosilicates at the phase boundary leads to the increasing of the strength of the concrete. This provides growth of operational properties. The high-strength lightweight concrete with an average density less than 1500 kg/m(3) is characterized by a strength more than 40 MPa (specific strength R-sp > 30 MPa). The optimum range of concentrations of the precursor for preparation of nano-modifier is defined to be 1.25 <= [Na+]/[Cl-] <= 2.5. We can conclude that the developed composition has a dense and strong structure which can resist intense cracking. Application of nanoscale modifier enables an increase of the elastic modulus of 13-36% (equal to 6.2-8.5 GPa depending on the average density), a decrease of water absorption (to 1%) and an improvement of the water resistance (coefficient of water resistance is more than 0.95) and freeze-thaw resistance (up to F300). The nano-modified high-strength lightweight concrete has beneficial values of heat-conduction coefficient (0.48-0.70 W/(m . degrees C)), temperature conductivity coefficient ((3.43-4.04).10(-7) m(2)/s) and specific heat capacity (1080-1175 J/(kg . degrees C)). It allows us to consider this concrete as a multifunctional material with both structural and thermal insulation properties.