The Promotion of Nano-SiO2 on the Compressive Strength of Alkali-Activated Materials

Nanomaterial which has high activity is widely used in the modification of cement-based materials due to its physical filling and chemical bonding. This paper mainly studied the influence of nano-SiO2 on the compressive strength of the alkali-activated materials, using XRD and SEM technology to analyze the mineral composition microstructure of alkali-activated materials, modification effect, etc. The results show that the doping of nano-SiO2 can enhance the compressive strength of alkali-activated materials. Under the condition of fixed water-binder ratio and alkali content, the optimum dosage of nano-SiO2 is 4%. When the content is 4%, the intensity of 28 days is increased by 26.81% compared with the blank sample, and compressive strength of 94.93 MPa is reached. By XRD and SEM, we can find a large number of CSH and a certain amount of CH in the sample. The promotion effect of nano-SiO2 on the alkali-activated materials provides a better support for the application of the alkaliactivated materials in reality

Effect of Nano-SiO2 Content on the Setting Time and Mechanical Properties of Tricalcium Silicate

Using analytically pure calcium carbonate and silica as raw materials, high purity tricalcium silicate (C3S) is prepared by solid-state reaction. The tricalcium silicate was sintered at a temperature of 1550°C with the heat preservation time of 6 h. The final sample needs three times of calcination circles. Ultrasonic cleaning machine was used to disperse the water and different amount of nano-SiO2 (0, 1, 2, and 3 wt%) for 5 min, then mixed with C3S, and formed into standard blocks. The setting time and compressive strength of each age (1, 3, 7, and 28 days) was measured to investigate the effect of nano-SiO2 on the setting time and mechanical properties of C3S. The results show that the content of free calcium oxide (f-CaO) in C3S sample is lower than 0.8% tested by glycol ethanol method sensitive, C3S crystal type is triclinic system T1 by X ray diffraction (XRD). The nano-SiO2 cut down the setting time of C3S and the setting time of C3S is decreasing with the increasing content of nano-SiO2. The initial setting time of C3S with different content of nano-SiO2 (0, 1, 2, and 3 wt%) are 187, 129, 105, and 85 min, respectively, the final setting time are 219, 194, 158, and 130 min. The addition of nano-SiO2 can significantly improve the early compressive strength of C3S, but the effect of nano-SiO2 on improving compressive strength of C3S is gradually weakened with the hydration of C3S

Influence of the Surface Treatment of Hardened Cement Mortar with Colloidal Nano-Silica and TEOS

Two types of silicate material, tetraethoxysilane (TEOS) and colloidal nanoSiO2 (CNS), were applied for surface treatment of hardened cement mortar by exploring their filling and pozzolanic reactivity to make the surface compacter. Results showed that the water adsorption coefficient, the water vapor transmission rate, and the water penetration depth were reduced when CNS and TEOS were applied onto the surface of hardened cement mortar, and TEOS exhibits a superior effect on surface treatment, making the mass-transport rate and extent smaller than CNS does

Influence of SiO2@PMHS on the Water Absorption of Cement Mortar as a Surface Treatment Agent

In this paper, the core–shell structured SiO2@PMHS hybrid nanoparticles were synthesized with tetraethoxysilane (TEOS) and polymethylhydrosiloxane (PMHS). And SiO2@PMHS core–shell nanoparticles were first used as a surface treatment agent for cement-based materials. The influence of SiO2@PMHS nanoparticles on the water absorption of hardened cement mortar with water-to-cement ratio of 0.6 was investigated. Results showed that the water absorption of cement mortar treated with SiO2@PMHS nanoparticles was decreased by 93.47% in comparison to the control sample

Design and Development of a New Lightweight High-speed Stacker

A new lightweight high-speed stacker is designed and developed. Its technical parameters are leading the industry level, which can meet the current requirements for high efficiency of intelligent logistics system. Starting from the key structure of stacker, through the theoretical analysis of the new mechanism and the comparison of the new and old equipment, the advantages of the new mechanism in improving the efficiency and lightweight design of stacker are explained. Through ANSYS Workbench finite element software, the structural strength of the main bearing mechanism is analyzed, and the results show that the strength meets the requirements

Effects of Nano-CaCO3 on the Properties of Cement Paste: Hardening Process and Shrinkage at Different Humidity Levels

The hardening process and volume stability of cement pastes with and without nano-CaCO3 (NC) were studied through investigations on the setting time and shrinkage. Results showed that NC shortened the setting time of cement paste: the initial setting time decreased by 3.9 and 11.1% when 1 and 3% NC were added, and the finial setting times were shortened by 6.2 and 15.2%, respectively. The shrinkage of cement paste was compensated by NC, and the effect was more obvious as more NC was added into the cement paste. Although the shrinkage decreased at the lower relative humidity, the degree of hydration of cement can be hindered owing to the lack of sufficient internal curing humidity. Considering the hydration of cement and the volume stability of structure, a high curing humidity was an important factor for improving the durability of NC-modified cement-based materials

The Effect of Nano-SiO2 Dispersed Methods on Mechanical Properties of Cement Mortar

Nano-SiO2 is added to the cement by using different dispersion methods, through the macroscopic mechanical properties to characterize its dispersion in the cement, it can be used to explore the best experimental process. The results show that the compressive strength of cement samples with different dispersion methods is different. When the physical dispersion method is used, the intensity is not improved, but the ultrasonic dispersion method is the smallest, and the dispersion of nano-SiO2 is -9.11%. When the surfactant is used as dispersant, the dispersion of nano-SiO2 by Naphthalene water reducer is the best, and the compressive strength is increased by 6.68%. By using polymeric dispersing agent, polyethylene glycol has a certain effect on the dispersion of nano-SiO2, but it has some damage to the cement (set-retarder, etc.). Based on the above experiments, we have obtained the best dispersion method, which uses ultrasonic dispersion, and also needs to add naphthalene water reducer

The Synergistic Effect of Nano-Silica with Slag on Frost Resistance of Concrete

The frost resistance of concrete is one of the most important factors for its durability. Supplementary cementitious materials could effectively improve the frost resistance of concrete. On this basis, the synergistic effect of nano-silica (NS) with slag on the frost resistance of concrete is better than the single, which was investigated. Nano-silica and slag were employed as a partial substitute of cement. The effect of these on the related indexes, including the mass loss, relative dynamic elastic modulus and porosity of concrete were measured after specified number of freeze and thaw cycles. Results show that the frost resistance of nano-silica modified concrete was obviously improved. The mass loss of control concrete was 2.5 % after 300 freeze-thaw cycles while that of the nano-silica modified concrete was as low as 1%. Further, the anti-freeze durability factor can reach up to 89.55% for the nano-silica modified concrete. The reasons are that the activity and nucleation effects of nano-silica accelerate the hydration of cement and the filling effect leads to more compact matrix. All of these made concrete better frost resistant. This was also proven by the porosity analysis. When the nano-silica was added, the total porosity of nano-silica modified concrete decreased from 14.57 % to 11.39 % compared with the control concrete. So, the synergistic effect of nanosilica with slag can enhance the frost resistance of concrete and improve its durability

The Illumination Model of the Valley Based on the Diffuse Reflect of Forest

In this paper, models are build to evaluate the impact of the forest on the valley’s illumination. Based on the assumes that all the light reach the ground comes from the diffuse reflection which comes from the sun directly and from the diffuse reflection of other points, One model is build to consider the impact of time and latitude on the direction of the sunlight. So we can get the direction of the sunlight at different time and latitude through the model. Besides, this paper develops a illumination model to evaluate the intensity of illumination of the ground. Combining the models above, this paper get a complete model which can not only evaluate the overall light intensity of the valley but also convert the light intensity to the intensity of illumination. Simulation of the intensity illumination of some basic terrains and finally gives a comprehensive results which is practical and close to the common sense

EFFLORESCENCE INHIBITION OF ALKALI-ACTIVATED STEEL SLAG-SLAG MATERIAL BY NANO SiO₂

Alkali-activated materials have significant shortcomings like poor volume soundness, easy efflorescence and so on, which have restricted their application to a certain degree. Nano modification is an important approach in solving the problem. Based on the test of hydration hardening characteristics, matrix porosity and the concentration of alkali ions leaching on the surface of the alkali-activated steel slag-slag material, the effects of the nano SiO₂ on matrix compaction and efflorescence inhibition were studied. The results show that when the mixing amount of the nano SiO₂ was 2.0%, the growth rates of the compressive strengths of the specimen at 1d and 28d increased by 203.71% and 39.29%, respectively, when compared with the blank specimen. The nano SiO₂ exerted filling and crystal nucleus effects, and a clustering fibrous C-S-H gel was generated around the nanoparticles. The matrix was compacted with an increase in the hydration products, and, as a result, the overall porosity of the matrix reduced by 7.06%. Porosity improvement contributed in preventing internal alkali ions in the specimen leaching to the surface, and the ionic concentration of the leaching solution out of the specimen reduced by 32.57% when compared with the blank specimen