Research on the Development of High Impact Resistant Preplaced Aggregate Fibrous Concrete by the Inclusion of Coarse Aggregates Coated with Asphalt

The Combined Effect of Glass Fiber Mesh and Steel Fiber on Two-Layered Preplaced Aggregate Concrete against Drop Weight Impact

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%.

Response of Functionally Graded Preplaced Aggregate Fibrous Concrete with Superior Impact Strength

This research examines the modified drop-mass impact performance on functionally graded preplaced aggregate fibrous concrete (FPAFC) against repeated low-velocity impacts. Three-layered FPAFCs were prepared with the outer layers reinforced with steel and polypropylene fibers to evaluate the impact resistance. For comparison, both one- and two-layered concretes were cast simultaneously. The modified version of the impact test was suggested to the ACI 544 drop-mass impact test to decrease the scattered test data. The modification was a replacement of the steel ball with a steel bar to apply a line impact instead of the single-point impact. This modification distributes the impact energy over a broader area and reduces the scattering of results. The study parameters for the tests were impact numbers, which cause first cracking and failure; ductility index; and mode of failure. In addition, three methods of the two-parameter Weibull distribution were used to examine the dispersed test results, which were presented in terms of reliability. Results revealed that the specimens comprising 3.6% steel fibers at the top layer and no fiber at the middle layer exhibited the highest percentage improvements of 633% and 2732% recorded for the cracking and failure impact number, respectively. The percentage difference in impact strength results between these two methods ranged from −14% to 75% for cracking impact number and from 6.8% to 57.2% for failure impact number. The coefficient of variation value calculated from the modified impact test was reduced and ranged from 20.3% to 56.1% for cracking impact number and from 15.2% to 65.3% for failure impact number, compared with the same mixtures from the ACI 544 test method. This phenomenon indicates that the modified impact test delivered a lower scattering of results by introducing a line of impact using a steel bar rather than a single-point impact.

Enhancing the Impact Strength of Prepacked Aggregate Fibrous Concrete Using Asphalt-Coated Aggregates

The brittleness of plain concrete represents a significant issue to the integrity of concrete structures when subjected to impact loading. Recent rapid industrialization has attracted researchers to find a solution for concrete brittleness and enhance its ductility. In light of this, the prepacked aggregate fibrous concrete (PAFC) with single and double precoated coarse aggregates using asphalt is proposed and examined. Nine different mixtures were designed using polypropylene and steel fibre of 3% dosage with single and double asphalt-coated aggregates. Specimens were prepared with natural aggregate and 100% C-graded asphalt-coated aggregate to evaluate their impact strength. The ACI Committee 544 drop-weight impact standard was followed in the testing of all specimens. Results indicated that using asphalt-coated aggregate can improve the impact energies of concrete. The impact energy at cracking and failure of the single asphalt-coated aggregate specimen was 1.55 and 2.11 times higher, while the double-coated aggregate specimens exhibited 1.73 and 2.56 times greater than the natural aggregate specimen, respectively. The contribution of fibres in enhancing the impact resistance is remarkable compared to the single- and double-coated aggregates used in PAFC.

Impact Resistance of Functionally Layered Two-Stage Fibrous Concrete

The impact resistance of functionally layered two-stage fibrous concrete (FLTSFC) prepared using the cement grout injection technique was examined in this study. The impact resistance of turtle shells served as the inspiration for the development of FLTSFC. Steel and polypropylene fibres are used in more significant quantities than usual in the outer layers of FLTSFC, resulting in significantly improved impact resistance. An experiment was carried out simultaneously to assess the efficacy of one-layered and two-layered concrete to assess the effectiveness of three-layered FLTSFC. When performing the drop-mass test ACI 544, a modified version of the impact test was suggested to reduce the scattered results. Instead of a solid cylindrical specimen with no notch, a line-notched specimen was used instead. This improvement allows for the pre-definition of a fracture route and the reduction of the scattering of results. The testing criteria used in the experiments were impact numbers associated to first crack and failure, mode of failure, and ductility index. The coefficient of variation of the ACI impact test was lowered due to the proposed change, indicating that the scattering of results was substantially reduced. This research contributes to the idea of developing enhanced, more impact-resistant fibre composites for use in possible protective structures in the future.