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Protective structures subjected to intensive loads that may benefit from the use of multilayer composite structures with excellent hardness and impact resistance represent an emerging research field in recent times. In this study, low-velocity projectile impact tests were performed on Functionally-graded Preplaced Aggregate Fibrous Concrete (FPAFC)...
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... second was macro polypropylene fibre (PF) with a diameter of 0.8 mm, length of 45 mm and tensile strength of 500 MPa. Figure 3 depicts the appearance of two different fibres that were utilized in this research. ...
Context 2
... the results of the two fibrous mixtures (S-SF and S-PF) for each needle configuration, it is obvious that the retained impact numbers by S-SF specimens were 2.2 to 2.7 times those of S-PF ones, which shows the explicit superior impact performance of SF over PF. The better performance of SF is attributed to its superior physical properties (tensile strength and elastic modulus) compared to PF and its deformed configuration and hooked ends (Figure 3). The higher tensile strength of SF (1150 MPa) compared to PF (500 MPa) increased the ability of the fibre to withstand higher range of tensile stresses across the two ends of cracks, resulting in better bridging activity by postponing the breakage of fibres. ...
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... Recently, there has been a proposal for the concept of "functionally graded concrete" owing to its high practicality and associated benefits [11,12]. The natural world provides diverse materials and structures that serve various purposes necessary to sustain living organisms. ...
Nowadays, cement manufacturing stands as the third most significant contributor to anthropo-genic CO 2 emissions. Alkali-activated techniques are emerging as a potentially more environmentally friendly alternate binder to mitigate the risks related to climate change. The current investigation utilizes the notion of preplaced aggregate concrete (PAC) and alkali-activated slag grouts comprising multi-walled carbon nanotubes (MWCNT) of 0.1 % dosage to implement functionally graded preplaced aggregate fibrous concrete slabs (FGPAFC). The optimum efflux time of alkali-activated slag grouts was determined through trials with various superplasticizer dosages and water-to-binder ratios. However, as it has not been investigated previously, the effect of alkali-activated grout made up of MWCNT on the impact strength of the FGPAFC slab deserves special focus. For this, seven different slabs were prepared, in which five three-layered FGPAFC slabs containing a steel fibre at a dosage of 3.5-4.5 % at a 0.25 % increment were provided at the upper and lower layers. At the same time, the middle layer contains 0-2 % fibres at 0.5 % increment. Using the same amount of fibre as in FGPAFC, a PAC slab with uniform fibre distribution is made to examine how effectively the three-layer arrangement performs. The slab underwent an impact test in accordance with the guidelines set forth by ACI Committee 544. The cracking and failure impact number, crack resistance at service and ultimate stages, impact ductility, the ratio of crack resistance, failure pattern, and its mechanism were examined. Findings reveal that the cracking and failure impact energies were enhanced by roughly 3-12 % and 15-53 %, respectively, by lowering the fibre content at the middle layer and raising it at the upper and lower layers of the FGPAFC slab from 3.0 progressively to 4.5 %. The contribution of steel fibre is more significant than MWCNT for enriching the impact resistance of FGPAFC. The findings derived from this study offer foundational data for subsequent comprehensive scientific examination of FPAFC subjected to impact.
... Because of its bridging function, this sort of fibre would make it less likely that cracks would start appearing due to the stresses caused by external loads [35]. Because of the activity of fibers in bridging, cracks were prevented from enlarging and spreading further, and their opening to the exterior surfaces was postponed [36]. The material began to crack at the microstructural stage after only a few strikes, and this happened very quickly, which with increasing tension, was found to exhibit multi-cracking behavior. ...
... There are many different kinds of short fibers on the market right now, but their high price tags and huge carbon footprints provide significant economic and sustainability challenges [24][25][26]. To counteract the brittleness of the matrix-forming fiber-reinforced concretes (FRCs), researchers may add fibers [24,[27][28][29][30][31]. FRC composites are relatively new, ground-breaking, and sustainable with a number of advantages, such as high flexural and tensile strengths, the ability to form various structural configurations under various loading conditions, and the capacity to stay untouched for lengthy periods of time without repair works. ...
The aim of the paper is to development of basalt fiber-reinforced high-strength eco-friendly concrete with modified composite binder for sustainable construction. Cement composites based on a modified polymineral binder with the use of enriched aluminosilicates obtained from coal ash have been developed. A technology has been developed for extracting aluminosilicates from coal ash, which includes five stages. The choice of grinding technology of modified composite binder in a vario-planetary mill up to 550 m 2 /kg has been made, where the combined action of high impact energy, strong friction and centrifugal forces achieves the maximum mechanical activation of the binder. The developed fresh mixes are characterized by good flow-ability (slump 20 cm and slump flow 47-49 cm). The resulting composites are characterized by high 28-day compressive and flexural strengths of 59.1 and 13.3 MPa, respectively, which is 44% and 66% higher than that of the control sample. At the same time, the high ratio of 28-day flexural and compressive strengths, reaching 0.31 (for the control sample 0.19), proves the high potential of this material to work under shock and dynamic complex loading. These trends are also preserved for the ages of 1 and 7 days, which allows us to speak about the high early strength of the materials. Microstructural analysis using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy showed that the modified cement matrix has a denser microstructure with a large amount of low-basic calcium silicate hydrates (C-S-H), while the reference cement paste contains more high-basic C-S-H and hexagonal portlandite plates. The formed materials are able to withstand up to 15 thermal cycles at a temperature of 700 • С (4 times higher than that of the control sample), 13 thermal cycles at a temperature of 900 • С (4.3 times higher), 8 thermal cycles at a temperature of 1100 • С (exceeding eight times the characteristics of the unmodified sample, which is destroyed without enduring a single thermal change).
... Thus, the scenario of repeated impacts from fallen parts and objects is expected on already fire-deteriorated concrete structural parts at lower levels. Despite the need to understand the behavior of concrete members under the dual accidental loading of fire and low-velocity repeated impact, very few studies attempted to investigate this issue, and the focus of most of the research was on explosive [86][87][88][89] and projectile [90][91][92][93][94] impacts. To better understand the response of concrete structures to such a loading scenario, an experiment was conducted in this study, where conventional concrete with moderate strength was adopted, which is the most widely adopted type of concrete in traditional residential and civil structures, aiming to fill some gaps of knowledge in this area. ...
The response of plain and fibrous concrete to the scenario of fired structures exposed to
repeated impacts from falling fragmented building elements and other objects is experimentally
investigated in this study. The experimental program included the casting and testing of specimens
with 0%, 0.5%, and 1.0% hooked-end steel fibers (SFs) under the ACI 544-2R repeated-impact test.
The impact test was conducted using cylindrical disk specimens, while 100 mm cubes were used to
evaluate the residual compressive strength and weight loss. From each mixture, six disks and three
cubes were heated to high temperatures of 200, 400, and 600 �C, while a similar set of specimens were
tested without heating as a reference group. The results show that SF could significantly improve
cracking impact resistance and dramatically boost failure impact numbers. The retained percentage
improvements were the highest for specimens heated to 600 �C, which were approximately 250% at
the cracking stage and 1680% at the failure stage for specimens with 1.0% SF. The test results also
show that the repeated-impact resistance dramatically deteriorated at high temperatures, where the
maximal residual cracking and failure impact numbers after exposure to 200, 400, and 600 �C were
approximately 20% and 40%, 4% and 7%, and 2.2% and 4%, respectively.
... This provides an increase in adhesion between the fresh cement matrix and aggregate grains of different fractions and nature, which can be arranged in a row according to the strength of the solution: quartz < limestone < clinker. Due to this, products prepared using concrete scrap improved physical and mechanical properties, including crack resistance and resistance to dynamic loads [30][31][32][33][34]. ...
Due to renovation and fighting in the world, a huge accumulation of construction and demolition waste is formed. These materials are effectively used as aggregates, but there is very little information about the use of scrap concrete to create cementless binders. The purpose of the work is to be a comprehensive study of the composition and properties of concrete wastes of various fractions with the aim of their rational use as cementless binders. The scientific novelty lies in the fact that the nature of the processes of structure formation of a cementless binder based on sandy fractions of the screening of fragments of destroyed buildings and structures, as a complex polyfunctional system, has been theoretically substantiated and experimentally confirmed. Different percentages of non-hydrated clinker minerals in concrete scrap were determined. In the smallest fraction (less than 0.16 mm), more than 20% of alite and belite are present. Waste of the old cement paste is more susceptible to crushing compared to the large aggregate embedded in it, therefore, particles of the old cement paste and fine aggregate predominate in the finer fractions of the waste. Comprehensive microstructural studies have been carried out on the possibility of using concrete scrap as a completely cementless binder using scanning electron microscopy, X-ray diffraction analysis, and differential thermal analysis. It has been established that for cementless samples prepared from the smallest fractions (less than 0.315 mm), the compressive strength is 1.5–2 times higher than for samples from larger fractions. This is due to the increased content of clinker minerals in their composition. The compressive strength of the cementless binder after 28 days (7.8 MPa), as well as the early compressive strength at the age of 1 day after steaming (5.9 MPa), make it possible to effectively use these materials for enclosing building structures.
... The bridging and strengthening of cracks are responsible for this action [34]. The behavior of PAFC under compression is consistent with the earlier studies [35][36][37]. Because of issues about workability and maintaining a uniform dispersion of fiber, the amount of fiber that may be used in PAFC is typically limited to 2%. ...
Buildings and other infrastructure should be designed to withstand impact loads in terrorist
attacks or industrial catastrophes. Fibrous concrete is utilized in a variety of ways in the construction
of structures to resist impact loads. Preplaced aggregate fibrous concrete (PAFC) has a different
production method than traditional fibrous concrete. Although PAFC offers several benefits over
standard fibers in the construction of protective structures, there are relatively few investigations on
the behavior of PAFC when exposed to impact loads. This research investigated the impact response
of PFAC with the combined action of steel fibers and glass fiber mesh (GFM). Twenty-two mixtures
were prepared and divided into two groups in which there were fibrous and non-fibrous specimens.
The specimens from the first group comprised various diameters (ratio of reinforcement surface
to total sample surface) of GFM and were provided in two and four layers. The second group of
specimens is the same as the first group, including a 3% dosage of steel fibers. All specimens were
subjected to a drop-weight impact test and the key parameters examined were cracking and failure
impact energies, ductility index and failure pattern. The results indicated that the incorporation of
GFM increased the impact performance and impact ductility, where the retained impact energies and
the ductility index increased by increasing the ratio of reinforcement surface (diameter) of GFM and
its number of layers. However, the positive influence of SF in enhancing the impact performance was
way higher than that of GFM. The use of 3% hooked-end SF improved the failure impact energy by
more than 3000%, while the maximum improvement gained by using four layers of 150 mm diameter
(full reinforcement surface) GFM was approximately 400%.
... Such a type of test is an expensive one and is intended to be performed on moderate-to large-scale test structural elements (beams or slabs), and is a very useful technique to study structural response under the effect of heavy falling objects [25][26][27][28][29]. Another common impact test is the Charpy pendulum test that is used to estimate the effect of impact forces on different sizes of elements that are made of different types of materials [20][21][22][23][24][25][26][27][28][29][30][31][32]. On the other hand, projectile [33][34][35][36][37] and explosive impacts [38,39] are also types of impact forces that are investigated using special, very costly techniques. None of the mentioned tests consider repeated impact influence and none can be termed as simple or low-cost testing methods. ...
With the aim of investigating the response of concrete to the dual effect of accidental fire high temperatures and possible induced impacts due to falling fragmented or burst parts or objects, an experimental work is conducted in this study to explore the influence of exposure to temperatures of 200, 400 and 600 °C on the responses of concrete specimens subjected to impact loads. Cylindrical specimens are tested using the recommended repeated impact procedure of the ACI 544-2R test. Three concrete mixtures with concrete nominal design strengths of 20, 40 and 80 MPa are introduced to represent different levels of concrete strength. From each concrete mixture, 24 cylinders and 12 cubes are prepared to evaluate the residual impact resistance and compressive strength. Six cylindrical specimens and three cubes from each concrete mixture are heated to each of the three levels of high temperatures, while the other six cylinders and three cubes are tested without heating as reference specimens. The test results show that the behavior of impact resistance is completely different from that of compressive strength after exposure to high temperatures ; the cylindrical specimens lose more than 80% of the cracking and failure impact resistance after exposure to 200 °C, while impact resistance almost vanishes after exposure to 400 and 600 °C. Concrete compressive strength is found to be effective on the unheated impact specimens, where the higher-strength cylinders retain significantly higher impact numbers. This effect noticeably decreases after exposure to 200 and 400 °C, and vanishes after exposure to 600 °C.
... The plastic region in the load-displacement curves of members under bending loads is calculated for the post-yielding region, which starts from the yielding point of the tension reinforcement to failure. This definition was also facilitated to investigate the effect of fibres and other additives on the post-cracking behaviour of disk specimens subjected to the ACI 544-2R repeated impact, where several previous studies [67][68][69][70] defined the impact ductility index as the ratio of the failure number to the cracking number (T2/T1). This study also adopted this definition to evaluate the influence of crumb rubber and SF on the enhancement of the failure impact resistance. ...
... The percentage developments in the impact ductility due to SF only were in the range of approximately 94 to 106%, which is much higher than that obtained due to crumb rubber. This result is attributed to the main function of SF as crack bridging elements that become fully functional after cracking, which boosts the failure impact numbers compared to their corresponding cracking numbers, resulting in higher ductility [70]. Finally, the combined effect of SF and crumb rubber can be calculated by comparing the ductility indices of the fibrous mixtures R5-F, R10-F, R15-F and R20-F with the ductility index of the reference plain mixture R0. ...
The proper disposal of used rubber tires has emerged as a primary concern for the environment all over the globe. Millions of tires are thrown away, buried and discarded every year, posing a major environmental concern owing to their slow decomposition. As a result, it is advantageous to use recycled waste rubber aggregates as an additional building resource. Recycling crushed rubber would lead to a long-term solution to the problem of decreasing natural aggregate resources while conserving the environment. This study examines the impact strength variability and reliability of preplaced aggregate concrete containing crumped rubber and fibres. Ten different mixtures were prepared by replacing natural aggregate with crumped rubber (5, 10, 15 and 20%). The crumped rubber was pretreated by the water with sodium hydroxide dilution for 30 min before usage. Hooked-end steel fibres were used at a dosage of 1.5%. The compressive strength, impact strength, impact ductility index and failure pattern were examined and discussed. In addition, a statistical method called Weibull distribution is used to analyze the scattered experimental results. The results showed that when the crumb rubber content was raised, the retained first cracking and failure impact numbers increased. As a result of substituting crumb rubber for 20% of the coarse aggregate in plain and fibrous mixes, the percentage development in first crack and failure was between 33 and 76% and 75 to 129%, respectively.
... Prasad et al. [11] evaluated the performance of functionally graded preplaced aggregate fibrous concrete (FPAFC) via the low-velocity projectile impact tests. The bioinspiration of the excellent impact strength of turtle shells was used to design an FPAFC comprising a higher amount of steel and polypropylene fibers at the outer layers. ...
Our civilization has used construction materials extensively, especially for infrastructure projects [...]
... Other possible sources of impact forces can be projectiles and fragmented parts from explosions in conflict areas or due to terrorist attacks [6,7]. The latter can be assessed using special high-velocity impact tests that simulate the effect of projectile hits, among which are the blast test [8][9][10][11][12] and projectile impact test [13][14][15][16][17][18]. On the other hand, for low-velocity impact tests, the ACI 544-2R [19] defined three major test procedures. ...
The ACI 544-2R introduced a qualitative test to compare the impact resistance of fibrous concretes under repeated falling-mass impact loads, which is considered to be a low-cost, quick solution for material-scale impact tests owing to the simplified apparatus, test setup and procedure, where none of the usual sophisticated sensors and data acquisition systems are required. However, previous studies showed that the test results are highly scattered with noticeably unacceptable variations, which encouraged researchers to try to use statistical tools to analyze the scattering of results and suggest modifications to reduce this unfavorable disadvantage. The current article introduces a state-of-the-art literature review on the previous and recent research on repeated impact testing of different types of fibrous concrete using the ACI 544-2R test, while focusing on the scattering of results and highlighting the adopted statistical distributions to analyze this scattering. The influence of different mixture parameters on the variation of the cracking and failure impact results is also investigated based on data from the literature. Finally, the article highlights and discusses the literature suggestions to modify the test specimen, apparatus and procedure to reduce the scattering of results in the ACI 544-2R repeated impact test. The conducted analyses showed that material parameters such as binder, aggregate and water contents in addition to the maximum size of aggregate have no effect on the variation of test results, while increasing the fiber content was found to have some positive influence on decreasing this variation. The survey conducted in this study also showed that the test can be modified to lower the unfavorable variations of impact and failure results.
