Presence Of Polypropylene Fibers Research Articles

Verifying domain knowledge and theories on Fire-induced spalling of concrete through eXplainable artificial intelligence

• Spalling theories and domain knowledge were verified for the first time using XAI. • XAI is an effective to gain new insights into the spalling phenomenon. • Recommendations for concrete mixtures with low tendency to spall under fire are proposed. This paper adopts eXplainable Artificial Intelligence (XAI) to identify the key factors influencing fire-induced spalling of concrete and to extract new insights into the phenomenon of spalling by investigating over 640 fire tests. In this pursuit, an XAI model was developed, validated, and then augmented with two explainability measures, namely, Shapley Additive exPlanations (SHAP) and Local eXplainable model-agnostic explanations (LIME). The proposed XAI model not only can predict the fire-induced spalling with high accuracy (i.e., >92 %) but can also articulate the reasoning behind its predictions (as in, the proposed model can specify the rationale for each prediction instance); thus, providing us with valuable insights into the factors, as well as relationships between these factors, leading to spalling. Our findings indicate that there are eight key factors that heavily govern spalling: 1) presence of Polypropylene fibers, 2) degree of moisture content, 3) heating rate, 4) maximum exposure temperature, 5) silica fume/binder ratio, 6) sand/binder ratio, 7) water/binder ratio and 8) fly ash/binder ratio. While these factors were also listed by the majority of the existing spalling theories, the contribution of each factor seems to vary significantly and, most importantly, was not quantified for the most part. Thus, the validated model was then utilized to contrast and quantify the spalling-based knowledge domain and theories as collected by some of the most cited studies in this domain.

Synthesis, characterization and mechanical study of polypropylene polymer based reinforced concrete with different admixture

We have fabricated two different concrete based on polypropylene fibers with three different percentage admixture and water repellent dosages. The mortar mixtures were proportioned with cement to sand ratio of 1:3 and 1:4. The important FTIR peaks indicates that the presence of polypropylene fibers, and water repellent silicon in concrete mixture. The XRD spectra confirmed that the angle 2th value with corresponding planes are because of mainly tetrahedrally arranged silicate and octahedrally arrangement of aluminate groups in mixed concrete. The reinforced concretes were cast for the same flow level but different percentages of polypropylene fibers (0, 5, 10 & 15%) dosage. The mechanical study proves that the compressive strength and tensile strength of the concretes increases with increase in polypropylene based concrete mixtures up to 10 wt %. However, it is also noted that the admixture significantly enhances the mechanical strength and decreases the early shrinkage of the concrete.

Mechanical Properties of Engineered Cementitious Composite Materials Using Different Types of Fibers

An Engineered Cementitious composite is an ultra ductile cementitious composite which is highly crack resistant, with a tensile strain capacity over that of normal concrete. In this study, three different types of PP. fibers are added to cement mortars with the aim to determine how they can be used to develop ECC materials. Fibers are used in different (aspect ratio, tensile strength and different proportions in volume fraction (1.0, 2.0, 3.0 and 4%)) in concrete mixture design. Hardened concrete properties, 28-days splitting tensile strength, flexural strength, cracking width were evaluated. Statistically significant effects were observed for polypropylene fibers on the splitting tensile and flexural strength, toughness indexes, and durability parameters showed an increase in the presence of polypropylene fibers. Increased fiber availability (fiber aspect ratio) in the concrete matrix, in addition to the ability of longer polypropylene fibers to bridge on the micro cracks, are suggested as the reasons for the enhancement in mechanical properties. Finally, crack width in fiber-reinforced concrete is calculated analytically with fiber property variables (fiber type, length, diameter and proportion). Results are compared with experimental values and concluded that with an increase in fiber length and/or decrease in fiber diameter crack width, decrease significantly

Cohesive stress and fiber pullout behavior in fracture response of concrete with steel and macropolypropylene hybrid fiber blends

AbstractThe fracture behavior of concrete with steel and macropolypropylene hybrid fiber blends (HyFRC) is evaluated and compared with steel fiber reinforced concrete (SFRC). Fiber blends at identical volume fraction as SFRC are shown to produce an improvement in the fracture response. At small crack separation, immediately after cracking, higher cohesive stress is produced in HyFRC compared to SFRC. Polypropylene fibers in concrete contribute cohesive stresses at larger crack separation. Polypropylene fibers in the concrete matrix improve the efficiency of the steel fibers by mobilizing a higher resistance at the initiation of the pullout. The initial stiffness, peak load, and the residual frictional resistance of the steel fiber pullout are increased with the addition of the polypropylene fibers. The higher reinforcing efficiency of steel fibers in the presence of polypropylene fibers is due to improved fiber–matrix bond, which results in a higher cohesive stress at smaller crack openings.

Sustainable Use of Waste Polypropylene Fibres to Enhance the Abrasion and Skid Resistance of Two-Stage Concrete

Two-stage concrete (TSC), also known as prepacked aggregate concrete (PAC), differs from traditional concrete in terms of site application and manufacturing process. Although this type of concrete is not a replacement for conventional concrete applications, it is an ideal option for unusual and difficult placing conditions, especially for repairing existing concrete structures. In other words, this type of concrete is a newly developed concrete and made by placing and packing coarse aggregates and fibres in a designed formwork, then injecting a cement grout mixture into the free spaces between the aggregate particles using gravity or a pump device. For the mentioned system and others, concrete components used as floors or pavements must have an adequate degree of roughness during service life when exposed to skid and abrasion. Thus, this research work introduced a new concrete method (prepacked aggregates fibre-reinforced concrete—PAFRC) with high abrasion and skid resistance reinforced with waste polypropylene (PP) fibres from the carpet industry. The effects of PP fibres at 0–1% dosages on the mechanical properties, abrasion resistance, and skid resistance of PAFRC mixes were studied. The results revealed that the addition of PP fibres reduces the compressive strength of concrete mixtures. Nonetheless, the presence of PP fibres results in PAFRC mixes having higher tensile strength, abrasion resistance, and skid resistance than plain concrete. It was detected that in both grouting methods (gravity and pump), with the addition of PP fibre up to a specific dosage, the resistance against abrasion and skid was increased by about 26% compared to plain PAC mix. Additionally, the outcomes indicated that PAFRC is a promising material for applications such as pavements with high abrasion and skid resistance.

Fresh Properties of Fiber Reinforced Cement-Based Foam with Pozzolans

This paper investigates the fresh properties of cement-based foam reinforced with fibers and examines the influence on density, pozzolan, spreadability, and flowability. Here, marsh and flow cone testing were employed for measuring the flowability and spreadability. This testing was conducted on seven series of cement-based foam mixtures prepared by adding polypropylene (PP) microfibers at the volume fraction of 0.2% in 800, 600, and 400 kg/m3 cast densities. In six series, the 10% and 20% of cement were replaced by fly ash, silica fume, and metakaolin, respectively. The results showed that the slurry flow time increases in the presence of polypropylene fibers and pozzolans, with metakaolin blended mixtures, recorded the longest time. Similarly, an increase in the foam volume was noticed in all mixtures except for the metakaolin series with higher substitution. Also, it was observed that the spread diameter reduces in fiber reinforced cement-based foam mixtures, but for fly ash series increase was noticed. Based on these results, models were developed for predicting the foam volume and spreadability for mixtures with pozzolan and polypropylene fibers.

Effect of thermal damage on mechanical behavior and transport properties of self-compacting concrete incorporating polypropylene fibers

Explosive spalling of cementitious composites when it is heated from surface is considered to be the most dangerous effect of damage of concrete structures subjected to fire attack, especially when it occurs in restricted areas such as underground tunnels. The main objective of the study presented in this paper is to investigate the influence of high temperature on mechanical behavior, pore size distribution and transport properties of self-compacting concrete reinforced with polypropylene fibers (PPF). The experiment investigation was carried out using two mixtures with a constant water-to-binder ratio (w/b) of 0.37. Two SCCs mixtures were manufactured using an industrial cements according to European standard EN 197 1: CEM I 52.5 N (Portland cement), the difference between the mixtures is the presence of PPF. The amount of fibers used was fixed in 2 kg/m3, as recommends Eurocode 2 for high performance concrete to avoid explosive spalling. The specimens were subjected to various heating-cooling cycles from the room temperature 20 °C to 200 °C, 300 °C, 400 °C and 500 °C. The chloride resistance of the two SCC produced with the different mixtures in damaged and undamaged state are measured using a chloride migration test accelerated by an external applied electrical field. Intrinsic permeability is measured using the nitrogen gas. Klinkenberg approach is used for the determination of the intrinsic permeability. Torrent permeability measurement method was applied in this article, and a correlation was obtained between measure of intrinsic permeability and the Torrent permeability measurement. Finally, a relationship between thermal damage indicators and the increase in permeability and migration coefficients is also obtained.

Akustična in elektromagnetna emisija lahkega betona s polipropilenskimi vlakni

This paper is focused on failure monitoring in lightweight concrete (special high-performance concrete that contains porous aggregate with a low bulk density) with high-strength polypropylene fibers under mechanical loading. The aim was to determine how the cracks’ generation intensity in the tested concrete samples depends on the fibers’ length and quantity. Our diagnostic method is based on a measurement of the acoustic and electromagnetic emission signals, which occur when solid dielectric materials are mechanically stressed. Several groups of lightweight concrete samples with various types and concentrations of high-strength polypropylene fibers were prepared for our experiment. We made two-channel measurements of the concrete samples from each group for defined loading conditions. The first channel was electromagnetic emission (EME) and the second was acoustic emission (AE). The electromagnetic emission and acoustic emission methods are promising methods to study the generation and behavior of cracks. The main advantage of EME and AE is their ability to be detected already in the stressed stage, which prevents macroscopic deterioration in solids. From the obtained results it can be concluded that the generated cracks’ intensity is significantly affected by the presence of polypropylene fibers and by their length and dosage.

Investigation of Cell Structure and Expansion Ratio of Microcellular Polypropylene Nanohomocomposites Prepared by a Solid-State Process

Microcellular poly(propylene-ethylene) random copolymer (r-PP-PE)/nanoclay (nanocomposite) and r-PP-PE/nanoclay/polypropylene fibers (nanohomocomposite) were autoclave-foamed via a solid-state microcellular foaming process using supercritical N2 as a foaming agent. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as a compatibilizer. Amount of PP-g-MA to nanoclay was 3:1. This study investigated the effects of clay content and the presence of polypropylene fiber on the expansion ratio and cell morphology of the samples. The results indicated that nanoclay increased the expansion ratio of the samples, but the expansion ratio for nanohomocomposites was slightly lower than the nanocomposites. In addition, scanning electron microscopy (SEM) observation showed that the nanoclay decreased the cell size and increased the cell density, except for the nanocomposite with the highest nanoclay content, 3 wt%, which had larger cell size compared to the samples with 1.5 wt% nanoclay and less. On the other hand, the simultaneous presence of nanoclay and polypropylene fibers synergistically increased the cell nucleation effect; thus there was a dramatic increase in cell density. The Differential scanning calorimetry (DSC) analysis showed that the microcellular foaming process decreased the crystallinity of both types of samples.

Effects of Water Jet on Heat-Affected Concretes

The paper is dealing with the effects of flat high-speed water jet on concretes affected by high temperature. Research should help to correct use of water jet technology in repair works on concrete structures especially after wildfires in tunnels, underground garages, etc., which are exposed to enormous thermal stress. Four concrete mixtures were prepared for tests of interaction of water jet with concrete. The samples were exposed to 200°C and 600°C and for comparison one third of samples were left unaffected. It was found, that both lower traversing velocity (cutting speed) and higher water pressure led to removal of higher amount of concrete. Higher temperature loading caused decrease of concrete strength and thus easier removal of surface layers by water jet. Concrete mixtures with basalt aggregate demonstrate higher resistance against water jet penetration regardless thermal loading compared to mixture with standard granodiorite aggregate. Presence of polypropylene fibres has substantial influence on concrete strength properties, however only marginal impact on resistance against water jet penetration.

Utilizing polypropylene fibers to improve physical and mechanical properties of concrete

The influence of polypropylene fibers has been studied in different proportioning and fiber aspect ratios to improve physical and mechanical properties of fiber-reinforced concretes. Fibers are used in two different lengths (12 mm and 19 mm) and proportions (0.1% and 0.3%) in concrete mixture design. Hardened concrete properties, such as 7- and 28-day compressive strength, splitting tensile strength, flexural strength, water and air absorption, and restrained shrinkage cracking were evaluated.No statistically significant effects were observed for polypropylene fibers on the compressive strength of concrete, while toughness indexes, splitting tensile and flexural strength and durability parameters showed an increase in the presence of polypropylene fibers. Increased fiber availability (fiber aspect ratio) in the concrete matrix, in addition to the ability of longer polypropylene fibers to bridge on the micro cracks, are suggested as the reasons for the enhancement in mechanical properties. Finally, crack width in fiber-reinforced concrete is calculated analytically with fiber property variables (fiber type, length, diameter and proportion). Results are compared with experimental values and concluded that with an increase in fiber length and/or decrease in fiber diameter crack width, decrease significantly.

Response of High-Strength Concrete Columns under Design Fire Exposure

The behavior of RC columns, especially those fabricated from high-strength concrete (HSC), under design fire exposure is not well quantified. Results from fire resistance experiments on six RC columns are presented in this paper. The test variables include concrete strength (permeability), fire scenario, load ratio and the presence of polypropylene fibers in concrete mix. Data from these fire tests is used to validate a macroscopic finite element model specifically developed for tracing the fire response of RC columns. Results from fire tests and numerical studies are used to illustrate the comparative performance of HSC and normal-strength concrete (NSC) columns under design fire conditions. Results from fire experiments show that HSC columns exhibit lower fire resistance than that of NSC columns. However both HSC and NSC columns do not experience failure under most design fire scenarios. The addition of polypropylene fibers to concrete mitigates fire-induced spalling and enhances fire resistance of HSC columns.

Comparison of compressive and splitting tensile strength of high-strength concrete with and without polypropylene fibers heated to high temperatures

This paper presents the results of an extensive experimental study on the compressive and splitting tensile strength of high-strength concrete with and without polypropylene (PP) fibers after heating to 600 °C. Mixtures were prepared with water to cementitious materials ratios of 0.40, 0.35, and 0.30 containing silica fume at 0%, 6%, and 10% cement replacement and polypropylene fibers content of 0, 1, 2, and 3 kg/m 3. A severe strength loss was observed for all of the concretes after exposure to 600 °C, particularly the concretes containing silica fume despite their good mechanical properties at room temperature. The range of 300–600 °C was more critical for concrete having higher strength. The relative compressive strengths of concretes containing PP fibers were higher than those of concretes without PP fibers. The splitting tensile strength of concrete was more sensitive to high temperatures than the compressive strength. Furthermore, the presence of PP fibers was more effective for compressive strength than splitting tensile strength above 200 °C. Based on the test results, it can be concluded that the addition of 2 kg/m 3 PP fibers can significantly promote the residual mechanical properties of HSC during heating.

RESONANT FREQUENCY IN POLYPROPYLENE FIBRE REINFORCED CONCRETE (PFRC) WITH POZZOLANIC MATERIALS

In this study, the resonant frequency of polypropylene fibre reinforced concrete (PFRC) under three different curing conditions was investigated and the influences of fly ash (PFA) and silica fume (SF) on PFRC under the same curing condition were also studied. The experiments were carried out in the Heavy Laboratory of City University of Hong Kong. Four types of concrete mixes were tested. A total of 24 concrete specimens were prepared. Test results show that the resonant frequency can be affected by the presence of polypropylene fibres, partial replacement of cement by silica fume or pulverized fly ash, and curing condition.

RESONANT FREQUENCY IN POLYPROPYLENE FIBRE REINFORCED CONCRETE (PFRC) WITH POZZOLANIC MATERIALS

Abstract In this study, the resonant frequency of polypropylene fibre reinforced concrete (PFRC) under three different curing conditions was investigated and the influences of fly ash (PFA) and silica fume (SF) on PFRC under the same curing condition were also studied. The experiments were carried out in the Heavy Laboratory of City University of Hong Kong. Four types of concrete mixes were tested. A total of 24 concrete specimens were prepared. Test results show that the resonant frequency can be affected by the presence of polypropylene fibres, partial replacement of cement by silica fume or pulverized fly ash, and curing condition.

Mechanical properties of polypropylene fiber reinforced concrete and the effects of pozzolanic materials

A comprehensive set of experimental data were generated regarding the effects of collated fibrillated polypropylene fibers at relatively low volume fractions (below 0.3%) on the compressive, flexural and impact properties of concrete materials with different binder compositions. Statistical analysis of results produced reliable conclusions on the mechanical properties of polypropylene fiber reinforced, concrete and also on the interaction of fibers and pozzolanic admixtures in deciding these properties. Polypropylene fibers were observed to have no statistically significant effects on compressive or flexural strength of concrete, while flexural toughness and impact resistance showed an increase in the presence of polypropylene fibers. Positive interactions were also detected between fibers and pozzolans.