Influence of Nanoclay on the Properties and Morphology of Cement Mortar

Mohammad R. Irshidat,Mohammed H. Al-Saleh 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10

This paper investigates the impact of partial substitution of cement with hydrophilic nanoclay platelets on the mechanical properties, workability, consistency, water absorption and morphology of cement mortar. Cement mortar mixtures with various replacement ratios, 0.5%, 1%, and 2% of nanoclay by weight of cement, were prepared and tested according to the standards. The results show that adding small quantities of nanoclay could improve the mechanical strengths of cement mortar. The best enhancements were reported for cement mortar reinforced with 2 wt.% nanoclay, where 11%, 5%, and 9% improvement in the compressive strength, flexural strength, and tensile strength, respectively, were observed. Adding nanoclay into cement mortar also leads to increase the amount of water needed to reach the normal consistency, elongate its setting time, increase its water absorption, but reduce its capillary water absorption coefficient and lower flowability of the pastes. SEM imaging showed a reasonable level of dispersion of nanoclay within the mortar.

Post-heating behavior of concrete beams reinforced with fiber reinforced polymer bars

Irshidat, Mohammad R.,Haddad, Rami H.,Almahmoud, Hanadi Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.6

The present paper investigates the post heating behavior of concrete beams reinforced with fiber reinforced polymer (FRP) bars, namely carbon fiber reinforced polymer (CFRP) bars and glass fiber reinforced polymer (GFRP) bars. Thirty rectangular concrete beams were prepared and cured for 28 days. Then, beams were either subjected (in duplicates) to elevated temperatures in the range (100 to $500^{\circ}C$) or left at room temperature before tested under four point loading for flexural response. Experimental results showed that beams, reinforced with CFRP and GFRP bars and subjected to temperatures below $300^{\circ}C$, showed better mechanical performance than that of corresponding ones with conventional reinforcing steel bars. The results also revealed that ultimate load capacity and stiffness pertaining to beams with FRP reinforcement decreased, yet their ultimate deflection and toughness increased with higher temperatures. All beams reinforced with FRP materials, except those post-heated to $500^{\circ}C$, failed by concrete crushing followed by tension failure of FRP bars.

Post-heating behavior of concrete beams reinforced with fiber reinforced polymer bars

Mohammad R. Irshidat,Rami H. Haddad,Hanadi Almahmoud 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.6

The present paper investigates the post heating behavior of concrete beams reinforced with fiber reinforced polymer (FRP) bars, namely carbon fiber reinforced polymer (CFRP) bars and glass fiber reinforced polymer (GFRP) bars. Thirty rectangular concrete beams were prepared and cured for 28 days. Then, beams were either subjected (in duplicates) to elevated temperatures in the range (100 to 500oC) or left at room temperature before tested under four point loading for flexural response. Experimental results showed that beams, reinforced with CFRP and GFRP bars and subjected to temperatures below 300oC,showed better mechanical performance than that of corresponding ones with conventional reinforcing steel bars. The results also revealed that ultimate load capacity and stiffness pertaining to beams with FRP reinforcement decreased, yet their ultimate deflection and toughness increased with higher temperatures. All beams reinforced with FRP materials, except those post-heated to 500oC, failed by concrete crushing followed by tension failure of FRP bars.

Microstructure and mechanical behavior of cementitious composites with multi-scale additives

Irshidat, Mohammad R.,Al-Nuaimi, Nasser,Rabie, Mohamed Techno-Press 2021 Advances in concrete construction Vol.11 No.2

This paper studies the effect of using multi-scale reinforcement additives on mechanical strengths, damage performance, microstructure, and water absorption of cementitious composites. Small dosages of carbon nanotubes (CNTs) or polypropylene (PP) microfibers; 0.05%, 0.1%, and 0.2% by weight of cement; were added either separately or simultaneously into cement mortar. The experimental results show the ability of these additives to enhance the mechanical behavior of the mortar. The best improvement in compressive and flexural strengths of cement mortar reaches 28% in the case of adding a combination of 0.1% CNTs and 0.2% PP fibers for compression, and a combination of 0.2% CNTs and 0.2% PP fibers for flexure. Adding CNTs does not change the brittle mode of failure of plain mortar whereas the presence of PP fibers changes it into ductile failure and clearly enhances the fracture energy of the specimens. Scanning electron microscopic (SEM) images of the fracture surfaces highlights the role of CNTs in improving the adhesion between the PP fibers and the hydration products and thus enhance the ability of the fibers to mitigate cracks propagation and to enhance the mechanical performance of the mortar.

Utilizing vacuum bagging process to enhance bond strength between FRP sheets and concrete

Nisrin R. Abdelal,Mohammad R. Irshidat 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.3

This paper investigates the effect of utilizing vacuum bagging process to enhance the bond behavior between fiber reinforced polymer (FRP) composites and concrete substrate. Sixty specimens were prepared and tested using double-shear bond test. The effect of various parameters such as vacuum, fiber type, and FRP sheet length and width on the bond strength were investigated. The experimental results revealed that utilizing vacuum leads to improve the bond behavior between FRP composites and concrete. Both the ultimate bond forces and the maximum displacements were enhanced when applying the vacuum which leads to reduction in the amount of FRP materials needed to achieve the required bond strength compared with the un-vacuumed specimens. The efficiency of the enhancement in bond behavior due to vacuum highly depends on the fiber type; using carbon fiber showed higher enhancement in the bond strength compared to the glass fiber when vacuum was applied. On the contrary, specimens with glass fiber showed higher enhancement in the maximum slippage compared to specimens with carbon fibers. Utilizing vacuum does not affect the debonding failure modes but lead to increase in the amount of attached concrete on the surface of the debonded FRP sheet.

Repair of Heat-Damaged RC Beams Using Micro-concrete Modified with Carbon Nanotubes

Wasim S. Barham,Mohammad R. Irshidat,Abdelrahman Awawdeh 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7

This paper investigates the use of micro-concrete modified with carbon nanotubes (CNTs) for the repair of heat-damaged reinforced concrete (RC) beams. Ten RC beams were cast and then subjected to elevated temperature of 550oC for two hours. The damaged beams were then repaired using micro-concrete integrating CNTs and tested under four-point bending. Different factors were taken into consideration in this research: CNTs modification, depth of repair, aggregate size of the repair material, and curing period. The repair material was applied on the tension side of the beam. Test results showed that micro-concrete with a larger aggregate size was more effective as a repair material than smaller sized aggregate micro-concrete. CNTs modification had little impact on the flexural strength of the repaired beams, but clearly enhanced the stiffness. The increase in the repair depth improved the strength recovery of the repaired beams but did not influence the failure mode. Curing period of the repaired beams significantly affected their stiffness but not their ultimate load and toughness. To investigate the mineral composition of repair material, scanning electron microscopy (SEM) was conducted for the micro-concrete with and without CNTs modified cementitious. The SEM image showed the CNTs are uniformly dispersed in the cement matrix. The CNTs and the products of the hydration process formed a meshwork structure. The CNTs acted as fillers to the voids, leading to an increase in the compressive strength.

Using ANN to predict post-heating mechanical properties of cementitious composites reinforced with multi-scale additives

Hashem K. Almashaqbeh,Mohammad R. Irshidat,Yacoub Najjar 국제구조공학회 2022 Smart Structures and Systems, An International Jou Vol.29 No.2

This paper focuses on predicting the post-heating mechanical properties of cementitious composites reinforced with multi-scale additives using the Artificial Neural Network (ANN) approach. A total of four different feed-forward ANN models are developed using 261 data sets collected from 18 published sources. The models are optimized using 12 input parameters selected based on a comprehensive literature review to predict the residual compressive strength, the residual flexural strengths, elastic modulus, and fracture energy of heat-damaged cementitious specimens. Furthermore, the ANN is employed to predict the impact of several variables including; the content of polypropylene (PP) microfibers and carbon nanotubes (CNTs) used in the concrete, mortar, or paste mix design, length of PP fibers, the average diameter of CNTs, and the average length of CNTs. The influence of the studied parameters is investigated at different heating levels ranged from 25°C to 800°C. The results demonstrate that the developed ANN models have a strong potential for predicting the mechanical properties of the heated cementitious composites based on the mixing ingredients in addition to the heating conditions.