Effect of Natural and Polypropylene Fibers on early Age Cracking of Mortars

Throughout time, the use of lignocellulosic resources has been implemented in the development of building materials. Among these resources, natural fibers are used as mineral binders reinforcement due to their specific mechanical properties. This experimental investigation focused on effect of flax and hemp fiber reinforcement on the resistance of pozzolanic-based mortars to cracking due to restrained plastic shrinkage. Results were compared with polypropylene fiber reinforcement and with control mortar without fibers. The quantity of fibers added to the mortar mix were respectively 0.25% - 0.5% by mass of binder for polypropylene fibers and 0.5% - 1% by mass of binder for flax and hemp fibers. All fibers have a similar length of 12 mm. The cracking sensitivity was evaluated based on two different methods: the first consists in casting the mortar in a metal mold with stress risers whose criteria are inspired by the ASTM standards. The second consists in pouring the mortar on a brick support. In order to assess the effect of fibers on cracking due to restrained plastic shrinkage, the number of cracks, total crack area and maximum crack width within the first 6 hours after casting were determined using digital image correlation (DIC). Results showed that the flax and hemp fibers were more effective in controlling restrained plastic shrinkage cracking compared to polypropylene fibers. With a natural fiber of 1% by mass of binder, maximum crack width was reduced by at least 70% relative to control mortar based specimens. Natural fibers show great ability to propensity for cracking due to restrained plastic shrinkage; so that, they could be an alternative and ecological solution for polypropylene fibers.

Investigation bending behaviors of the slabs with glass fiber reinforced polymer composite and steel bars

Glass fiber reinforced polymer (GFRP) composites have been frequently used in engineering applications in recent years. GFRP composites produced by using glass fiber and epoxy resin have significant advantages such as high strength, lightness, and resistance against corrosion. However, GFRP composites exhibit a more brittle behavior than steel bars. This study aims to investigate both the experimental and numerical bending behavior of slabs with GFRP bars, steel bars, and polypropylene fiber. Within the scope of experimental studies, 5 slabs were built. Two slabs called SS-1 and SS-2 have only steel bars. Two slabs called GFRPS-1 and GFRPS-2 have only GFRP composite bars. A slab called GFRPS-F has both GFRP composite bars and polypropylene fibers. Polypropylene fibers are added to fresh concrete to improve the slab’s ductility. Three-point bending tests have been carried out on the slabs. All slabs are subjected to monotonic increasing distributed loading until collapse. As a result of tests, GFRPS slabs have carried %53 higher load than SS slabs. However, the SS slabs have exhibited a more ductile behavior compared to the GFRPS slabs. GFRPS slabs have more and larger crack width than other slabs. The addition of 5% polypropylene fiber by volume to concrete has a significant contributed to ductility and tensile behavior of slab. The average displacement value of GFRPS-F slab is 22.3% larger than GFRPS slab. GFRPS-F slab has better energy consumption capacity than other slabs. The energy consumption capacity of GFRPS-F slab is 1.34 and 1.38 times that of SS and GFRPS slabs, respectively. The number of cracks in GFRPS-F slab is fewer than GFRPS slabs. The fibers have contributed to the serviceability of the GFRPS slabs by limiting the displacement and the crack width. GFRPS-F exhibits elastoplastic behavior and almost returns to its first position when the loading is stopped. In addition, experimental results are verified with numerical results obtained by using Abaqus software. Finally, it is concluded that GFRP composite bars can be safely used in field concretes, concrete roads, prefabricated panel walls, and slabs.

Utilization of EPS Beats and Polypropylene Fiber in Controlled Low Strength Material

Controlled low-strength material (CLSM) is a self-levelling cementitious material. It is not concrete nor soil-cement, however, it possesses properties similar to both. CLSM is widely used as a replacement for soil-cement material in many geotechnical applications such as structural backfill, pipeline beddings, void fill, pavement bases and bridge approaches. This paper study potential possibility of polypropylene fiber in CLSM. Harden and fresh properties compressive strength , flowability and density for the proposed CLSM were investigated. This CLSM mix design with different percentage of polypropylene fiber and pond ash, cement and water. EPS beats and polypropylene add 0 %, 0.5%, 1.0% and 1.5% of total weight is added in CLSM MIx. Results show that the CLSM incorporating EPS beats and polypropylene satisfies compressive strength requirement as per the requirements of ACI committee 229. polypropylene decreases the flowability of CLSM mix and at the same tine by adding EPS beats the density of CLSM mix are reduce which become lightweight CLSM mix. from this it can conclude that polypropylene fibers is less effective in CLSM mix and EPS beats make CLSM mix lightweight which create lightweight CLSM mix applicable for filling application.

3D-Printed Mortars with Combined Steel and Polypropylene Fibers

Fibers of various origins are of great importance for the manufacture of new generation cement composites. The use of modified composite binders allows these highly efficient building materials to be used for 3D-printing of structures for various functional purposes. In this article, changes in building codes are proposed, in particular, the concept of the rheological technological index (RTI) mixtures is introduced, the hardware and method for determining which will reproduce the key features of real processes. An instrument was developed to determine a RTI value. The mixes based on composite binders and combined steel and polypropylene fibers were created. The optimally designed composition made it possible to obtain composites with a compressive strength of 93 MPa and a tensile strength of 11 MPa. At the same time, improved durability characteristics were achieved, such as water absorption of 2.5% and the F300 frost resistance grade. The obtained fine-grained fiber-reinforced concrete composite is characterized by high adhesion strength of the fiber with the cement paste. The microstructure of the developed composite, and especially the interfacial transition zone, has a denser structure compared to traditional concrete. The obtained materials, due to their high strength characteristics due to the use of a composite binder and combined fiber, can be recommended for use in high-rise construction.