Effect of Sand Size on Mechanical Performance of Cement-Based Composite Containing PVA Fibers and Nano-SiO2

Effect of sand types and mixing procedures on the flexural behaviour of the high ductile mortar in monotonic and cyclic loadings

The use of fibre in concrete enhances its flexural behaviour and ductility. Different types of synthetic fibres are developed and replaced steel fibre to solve the corrosion of steel. Polyvinyl alcohol (PVA) is one of the synthetic fibres used in cementitious fibre composites. The High Ductile Mortar (HDM) was developed using PVA fibres. This paper assesses the effect of sand types and mixing procedures on the (PVA) fibre-reinforced high ductile mortar (HDM) in monotonic and cyclic loadings. Two different types of sands (crushed and river) and mixing methods were used for the comparison of the properties of HDM. The Pre-mixed mortar method refers to the mixing of PVA fibres in the pre-mixed mortar. And, pre-mixed paste method refers to the mixing of PVA fibres in a pre-mixed paste and the mixing of PVA mortar with the addition of sand. The pre-mixed mortar method gave a better flexural performance of the HDM than the pre-mixed paste method. The pre-mixed mortar method with crusher sand enhanced the flexural strength in the cyclic loading (11.8 MPa) than in the monotonic loading (10.3 MPa). It was the same for the case of river sand (11.4 MPa). Overall, the pre-mixed mortar method using river (finer) sand is better to enhance the strength, deflection, strain hardening, fracture energy, and toughness. The coarser sand is better for rigidity and fatigue flexural strength.

Improvements in the Engineering Properties of Cementitious Composites Using Nano-Sized Cement and Nano-Sized Additives

The findings of an extensive experimental research study on the usage of nano-sized cement powder and other additives combined to form cement-fine-aggregate matrices are discussed in this work. In the laboratory, dry and wet methods were used to create nano-sized cements. The influence of these nano-sized cements, nano-silica fumes, and nano-fly ash in different proportions was studied to the evaluate the engineering properties of the cement-fine-aggregate matrices concerning normal-sized, commercially available cement. The composites produced with modified cement-fine-aggregate matrices were subjected to microscopic-scale analyses using a petrographic microscope, a Scanning Electron Microscope (SEM), and a Transmission Electron Microscope (TEM). These studies unravelled the placement and behaviour of additives in controlling the engineering properties of the mix. The test results indicated that nano-cement and nano-sized particles improved the engineering properties of the hardened cement matrix. The wet-ground nano-cement showed the best result, 40 MPa 28th-day compressive strength, without mixing any additive compared with ordinary and dry-ground cements. The mix containing 50:50 normal and wet-ground cement exhibited 37.20 MPa 28th-day compressive strength. All other mixes with nano-sized dry cement, silica fume, and fly ash with different permutations and combinations gave better results than the normal-cement-fine-aggregate mix. The petrographic studies and the Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) analyses further validated the above findings. Statistical analyses and techniques such as correlation and stepwise multiple regression analysis were conducted to compose a predictive equation to calculate the 28th-day compressive strength. In addition to these methods, a repeated measures Analysis of Variance (ANOVA) was also implemented to analyse the statistically significant differences among three differently timed strength readings.

A Review of the Combined Effect of Fibers and Nano Materials on the Technical Performance of Mortar and Concrete

Nowadays, both nanomaterials and fibers have tremendous application in various industries, and they are a significant research area in the construction industry particularly. Thus, it is critical to have a comprehensive review to show the simultaneous impact of fibers and nanomaterials on the technical performance of different types of main construction materials such as mortar and concrete. The current work accomplishes this by providing a comprehensive review of the relevant literature on various nanomaterials and fibers through using a literate experimental database of conducted studies that have at least a type of fiber with one nanomaterial in the same mix. Accordingly, the collected data were analyzed, and they were compared to their control mixes in which no fiber and nanomaterials were used. The study majorly focuses on the effects of fibers and nanomaterials on fresh and hardened properties of produced mixes in terms of density, workability, mechanical and durability performance with consideration of microstructure and electrical resistivity as well. The study outcome provides a systematic knowledge and thorough guide to selecting and combining different fibers with nanoparticles to improve concrete/mortar performance effectively, in which not only the optimum percentage for the use of both fiber and nanomaterials are identified, but also is helpful to promote further research.

Effect of Incorporating Polyvinyl Alcohol Fiber on the Mechanical Properties of EICP-Treated Sand

Enzyme-induced calcium carbonate precipitation (EICP) technology can improve the strength of treated soil. But it also leads to remarkable brittleness of the soil. This study used polyvinyl alcohol (PVA) fiber combined with EICP to solidify sand. Through the unconfined compressive strength (UCS) test, the effect of PVA fiber incorporation on the mechanical properties of EICP-solidified sand was investigated; the distribution of CaCO₃ in the sample and the microstructure of fiber-reinforced EICP-treated sand were explored through the calcium carbonate content (CCC) test and microscopic experiment. Compared with the sand treated by EICP, the strength and stiffness of the sand reinforced by the fiber combined with EICP were greatly improved, and the ductility was also improved to a certain extent. However, the increase of CCC was extremely weak, and the inhomogeneity of CaCO₃ distribution was enlarged; the influence of fiber length on the UCS and CCC of the treated sand was greater than that of the fiber content. The improvement of EICP-solidified sand by PVA fiber was mainly due to the formation of a "fiber-CaCO₃-sand" spatial structure system through fiber bridging, not the increase of CCC.

Simulation of Bullet Fragmentation and Penetration in Granular Media

The aim of this work is to simulate the fragmentation of bullets impacted through granular media, in this case, sand. In order to validate the simulation, a group of experiments were conducted with the sand contained in two different box prototypes. The walls of the first box were constructed with fiberglass and the second with plywood. The prototypes were subjected to the impact force of bullets fired 15 m away from the box. After the shots, X-ray photographs were taken to observe the penetration depth. Transient numerical analyses were conducted to simulate these physical phenomena by using the smooth particle hydrodynamics (SPH) module of ANSYS^® 2019 AUTODYN software. Advantageously, this module considers the granular media as a group of uniform particles capable of transferring kinetic energy during the elastic collision component of an impact. The experimental results demonstrated a reduction in the maximum bullet kinetic energy of 2750 J to 100 J in 0.8 ms. The numerical results compared with the X-ray photographs showed similar results demonstrating the capability of sand to dissipate kinetic energy and the fragmentation of the bullet caused at the moment of impact.