Incorporation of nano TiO2 in black rice husk ash mortars

In this study, untreated black rice husk ash (BRHA) was employed as cement replacement in fractions of 10%, 20% and 30%. Dosages of 0.5%, 1.0% and 1.5% nano TiO2 were added into blended cement to study the mechanical properties and microstructural changes in mortars. The mechanical properties were studied using compressive and ultrasonic pulse velocity tests. XRD, SEM, TGA and DSC were conducted to investigate the chemical composition and microstructural changes of BRHA mortars with the presence of nano TiO2. The results showed that nano TiO2 in BRHA blended cement improved the mechanical properties and microstructure of BRHA mortars

Physical and chemical characteristics of unground palm oil fuel ash cement mortars with nanosilica

The present study focused on enhancing properties of unground palm oil fuel ash (UPOFA) mortars by incorporation of nanosilica (NS). To do so, 0.5–1.5% NS was admixed in each series of 10–30% UPOFA, respectively. The results revealed that incorporating NS offset the adverse effect of UPOFA on flowability, compressive strength and water absorption of mortars. Addition of NS increased the replacement level of UPOFA up to 20% with comparable compressive strength to control sample. SEM and XRD results showed that admixing NS led to improvement in the microstructure, and pozzolanic behavior of UPOFA mixtures at 28 days

The effect of nano silica on short term drying shrinkage of POFA cement mortars

This study investigates effects of nano silica on short-term drying shrinkage of mortars with palm oil fuel ash (POFA) during the first 28 days of curing. Furthermore, moisture content, hydration volume, and permeability were measured in order to study underlying mechanisms. It was revealed that addition of nano silica to samples with 30% POFA as cement replacement lowered the drying shrinkage by 7.5%. Also, it increased the strength development rate by 15% from 7 to 28 days of curing. Nano silica advantageously affected the shrinkage by refining the microstructure, increasing the hydration volume and lowering free water in cement matrix

Porous concrete pavement containing nanosilica from black rice husk ash

Rice husk is a waste from the agricultural industry. It has been found that the main inorganic element in rice husk is silica. Rice husk ash (RHA) as a replacement material in the conventional concrete mixture has been widely studied around the world. However, there is a lack of documented research on nano production from RHA used as a replacement cement in porous concrete pavement mixtures. This study employed the top-down approach via dry grinding in a mechanical ball mill to generate a nano-black RHA (nano-BRHA). As a result, nano-BRHA was successfully generated with an optimum duration of 63 hours and median size of 66 nm. The results also indicated that the particle size of BRHA was significantly decreased with increasing grinding time. In addition, the morphology of the nano-BRHA changed with grinding duration. Finally, the use of nano-BRHA produced porous concrete pavement with good strength and permeability, and sound absorption

Physical and chemical properties of unground palm oil fuel ash mortars incorporating Nano-SiO2

Abstract: Palm oil fuel ash (POFA) is an abundant agro-waste material obtained from palm oil process. The produced POFA in the mills has large particle size and porous structure which adversely affects the microstructure and pozzolanic reactivity of cementitious mixes, thus grinding process is suggested which can be considered as a physical treatment for morphology of original sized POFA. However, the purpose of this study was to overcome the detrimental effect of morphology of unground POFA (UPOFA) on cement mixtures by incorporation of small amount of nanosilica (NS). In particular, this study was aimed to investigate the effect of 0.5-1.5% NS on the physical and chemical properties of hardened cement mortars containing 10-30% UPOFA. Flowability of fresh samples, and mechanical properties (studied by compression and UPV tests) and microstructural changes (investigated by water absorption, permeable void ratio and SEM tests) of hardened mortars at 7, 28 and 90 days were examined to determine the physical properties of mixes. Furthermore, to trace the chemical composition changes of UPOFA cement mortars with and without NS, X-Ray difraction analysis (XRD) was carried out at 7 and 28 days, and thermo gravimetric analysis (TGA) was conducted at 90 days. The results revealed incorporation of NS compensated the adverse effect of UPOFA on the ow ability, mechanical properties and microstructure of mortars. Admixing only 0.5% NS increased the compressive strength of UPOFA by 11% higher than control sample at 28 days. Besides, incorporation of 0.5% NS augmented the replacement level of UPOFA up to 20% with almost comparable strength to control mortar. Microstructural studies indicated that admixing NS caused remarkable improvement in the porosity and density microstructure of the UPOFA mixes. Significant enrichment within ITZ microstructure of mixes was also observed from SEM images. Moreover, XRD pattern indicated that incorporating NS enhanced pozzolanic reactivity of UPOFA mortars which could further improve the density of matrix. However, no noteworthy enhancement in the compressive strength of UPOFA mortars with NS was observed at 90 days which was also verified by analyzing the CH content using TGA test. It was also observed that lower amount of NS was more effective at enhancing the properties of UPOFA mortars in the course of hydration

Engineered Cementitious Composite for Pavement Applications: Materials Development and Design Framework

Engineered Cementitious Composites (ECCs) are a novel class of high-performance fiber-reinforced cementitious composites characterized by their high tensile strain capacity. While ECCs have been presented as a promising material alternative for the construction of durable pavements and overlays, the cost of these materials is a major drawback, which limits their widespread implementation. More importantly, performance prediction models for ECC pavements existing in the literature are incomplete as the effect of ECC plasticity has not been considered in the integration of finite element (FE) analysis and beam flexural fatigue experimental test results. Moreover, the existing ECC pavements performance prediction models are generally limited to a single mixture design studied and cannot be generalized to other ECCs with various mechanical properties. Therefore, the objectives of this study are to (a) explore the possibility of developing cost-effective and practical ECC materials for pavement applications through reduction of fiber content and use of economical and widely available ingredients in the ECC production; (b) develop a novel thickness design framework considering the effects of ECC plasticity, and (c) develop thickness design equations for fatigue failure mode of ECC pavements considering ECCs’ elastic and plastic regimes as well as a broad range of mechanical properties. The research approach included experimental measurements and simulations using FE modeling. More cost-effective ECCs were developed by the use of more economical fibers at a reduced content, different types of locally available sand, and replacing fine aggregate and cement partially with crumb rubber and fly ash, respectively. Furthermore, a novel thickness design framework was developed by integrating three components of experimentally measured beam flexural fatigue performance models of ECCs, FE-quantified stress response of ECC pavements to vehicular loading, and a stress equivalency function. Finally, using the novel design framework, two general thickness design equations (both for the elastic and plastic regimes) were developed for ECCs with different mechanical properties. The findings of this study suggest that by implementing the proposed thickness design equations, a more accurate representation of the service life of ECC pavement is obtained during the plastic deformation regime in contrast to previous design frameworks proposed in the literature

Effects of nano TiO2 on properties of rice husk ash mortars

Abstract: The effect of nano TiO2 on untreated rice husk ash (RHA) mortars was investigated. The enhancement effect of treated RHA as a cement replacement on properties of cement composites has been extensively studied whereas the use of field burnt and untreated RHA has shown undesirable effect on the characteristics of cement-based materials due to the weak pozzolanic nature of untreated RHA. In this study, field burnt black rice husk ash denoted as BRHA was used as cement replacement in fractions of 10%, 20% and 30% of the mortar volume. To compensate the adverse effect of BRHA, 0.5%, 1% and 1.5% nano TiO2 were added into BRHA cement mortars. The mechanical properties were studied using the compression test and the results compared to a non-destructive method using ultrasonic pulse velocity at the age of 7, 28 and 90 days of curing. Water absorption and SEM tests were performed to study microstructural changes of hardened cement mortars at 7, 28 and 90 days. XRD, TGA and DSC tests were carried out to investigate the chemical composition of BRHA mortars with and without nano TiO2. The results indicated that incorporating nano TiO2 in blended cement with BRHA improved the mechanical properties and microstructure of BRHA mortars. Among the three different fractions of nano TiO2, addition of 1.5% nano TiO2 produced the highest value of compressive strength at all ages in comparison with 0.5% and 1% of nano TiO2-BRHA mixtures. For example, compressive strength of 10% BRHA mix with 1.5% nano TiO2 was 13% higher than that of control sample at 28 days. This was attributed to better particle packing of BRHA mortars with the presence of 1.5% nano TiO2. SEM images indeed showed improvement in the interfacial transition zone (ITZ) and density microstructure of BRHA mortars containing 1.5% nano TiO2. Moreover, a higher rate of pozzolanic activity of BRHA mortars was observed when 1.5% nano TiO2 was added. XRD results showed higher degree of CH consumption for BRHA mortars containing 1.5% nano TiO2 in comparison with BRHA mortars at 28 days. TGA results further confirmed the better pozzolanic behaviour for 1.5% nano TiO2-BRHA mixes compared to BRHA mixes with and without 0.5% and 1% nano TiO2. The results from DSC indicated that the well-crystalline structure of CH compound of BRHA mixes was transformed to the ill-crystalline phase when nano 1.5% TiO2 was added, which accounts for the superior pozzolanic activity of BRHA mortars with presence of 1.5% nano TiO2

Rejuvenation Mechanism of Asphalt Mixtures Modified with Crumb Rubber

Asphalt aging is one of the main factors causing asphalt pavements deterioration. Previous studies reported on some aging benefits of asphalt rubber mixtures through laboratory evaluation. A field observation of various pavement sections of crumb rubber modified asphalt friction courses (ARFC) in the Phoenix, Arizona area indicated an interesting pattern of transverse/reflective cracking. These ARFC courses were placed several years ago on existing jointed plain concrete pavements for highway noise mitigation. Over the years, the shoulders had very noticeable and extensive cracking over the joints; however, the driving lanes of the pavement showed less cracking formation in severity and extent. The issue with this phenomenon is that widely adopted theories that stem from continuum mechanics of materials and layered mechanics of pavement systems cannot directly explain this phenomenon. One hypothesis could be that traffic loads continually manipulate the pavement over time, which causes some maltenes (oils and resins) compounds absorbed in the crumb rubber particles to migrate out leading to rejuvenation of the mastic in the asphalt mixture. To investigate the validity of such a hypothesis, an experimental laboratory testing was undertaken to condition samples with and without dynamic loads at high temperatures. This was followed by creep compliance and indirect tensile strength testing. The results showed the higher creep for samples aged with dynamic loading compared to those aged without loading. Higher creep compliance was attributed to higher flexibility of samples due to the rejuvenation of the maltenes. This was also supported by the higher fracture energy results obtained for samples conditioned with dynamic loading from indirect tensile strength testing

Evaluation of the effects of engineered cementitious composites (ECC) plasticity on concrete pavement performance

Engineered Cementitious Composites (ECC) are considered a promising alternative for the construction of durable pavements. The objective of this study was to evaluate the effects of plasticity and flexural fatigue behaviour of ECC on pavement performance. A low-cost ECC using low fibre content (1.5% volume fraction), locally-available river sand and a high level of cement replacement with class F fly ash (75% by weight) was investigated. The ECC demonstrated a pseudo-strain-hardening (PSH) behaviour at all curing ages. Furthermore, as curing progressed, the tensile and flexural strengths increased; yet, ductility decreased. The flexural fatigue performance of the ECC was significantly superior to that of regular concrete. Finite Element Analysis (FEA) was integrated with flexural fatigue experimental results to establish a thickness vs. cycles to failure (T-N) relationship. In developing the T-N relation, the effect of ECC plasticity was accounted for by proposing a stress equivalency function to convert plastic stress into an equivalent linear elastic stress. From the T-N curves, it was determined that the original ECC T-N curve (without implementing the stress equivalency function) greatly overestimated the numbers of the cycle to failure for thicknesses below ~60 mm as this curve starts exhibiting an asymptotic behaviour with respect to N

Evaluation of cementitious matrices for the development of ultra-high performance engineered cementitious composites

The objective this study was to evaluate the compositional space of high-performance cementitious matrices using mostly readily available ingredients in region 6 for the development of ultra-high performance engineered cementitious composites (UHP-ECCs). Specifically, the present study evaluated the effects of supplementary cementitious materials (SCMs) to cement ratio (i.e., SCMs/C), silica fume to fly ash ratio (i.e., SF/FA), and ordinary sand to microsilica sand ratio (i.e., OS/MS) on the compressive strength (f\u27c) of cementitious matrices reinforced with 1 vol.% ultra-high-molecular-weight polyethylene (UHMWPE) fiber. The ratios of water to binder and sand to binder were kept constant at 0.24 and 0.3, respectively. A total of 36 mixtures were evaluated by compressive strength test. Experimental results showed that: (1) the increase in SF/FA enhanced f\u27c and SF/FA had the greatest impact on f\u27c; (2) the increase in SCMs/C produced a decrease in f\u27c; (3) the increase in OS/MS had a minor negative impact in f\u27c and OS/MS had the least impact in f\u27c from the variables studied