{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,13]],"date-time":"2026-10-13T12:58:20Z","timestamp":1791896300868,"version":"4.3.4"},"update-to":[{"DOI":"10.12688\/f1000research.175541.1","type":"new_version","label":"New version","source":"publisher","updated":{"date-parts":[[2026,3,19]],"date-time":"2026-03-19T00:00:00Z","timestamp":1773878400000}}],"reference-count":40,"publisher":"F1000 Research Ltd","license":[{"start":{"date-parts":[[2026,3,19]],"date-time":"2026-03-19T00:00:00Z","timestamp":1773878400000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["f1000research.com"],"crossmark-restriction":false},"short-container-title":["F1000Res"],"abstract":"<ns3:p>Background Cement-based materials deteriorate significantly when exposed to high temperatures due to extensive microcracking, increased porosity, and dehydration of hydration products, all of which lower the materials\u2019 mechanical performance and post-fire stability. This makes thermally robust mortar essential for protective applications in fire-prone areas as well as structural restoration. Method The goal of this study is to assess how the amount of polypropylene (PP) fiber in cement mortar affects its mechanical behavior, thermal resistance, and residual performance at temperatures as high as 600\u00b0C. Prior to and following exposure to increased temperatures of 200, 400, and 600\u00b0C, mortar mixes containing 0%, 0.5%, 1.0%, and 1.5% PP fibers by volume were made and tested for workability, density, compressive strength, flexural strength, and flexural toughness. Results The results show that increasing PP fiber content decreases workability. PP fibers significantly improved high-temperature performance. At 600\u00b0C, the control mix retained only 19% of its compressive strength, while the 0.5% PP mix retained 33%. Flexural strength increased by 26\u201344% at ambient temperature for 0.5\u20131.0% PP fiber content, and at 600\u00b0C, PP mixes preserved up to 8% more flexural strength than the control. Toughness improved substantially, with the 1.5% PP mix showing nearly 10-time higher residual toughness than the control at 600\u00b0C. Conclusions In conclusion, the incorporation of 0.5-1.0% polypropylene fibers provides a balanced enhancement in thermal resistance, residual strength and ductility, confirming its effectiveness in producing mortar with superior structural integrity after exposed to high temperatures.<\/ns3:p>","DOI":"10.12688\/f1000research.175541.2","type":"journal-article","created":{"date-parts":[[2026,3,19]],"date-time":"2026-03-19T13:54:09Z","timestamp":1773928449000},"page":"30","update-policy":"https:\/\/doi.org\/10.12688\/f1000research.crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Performance of Polypropylene Fiber-Reinforced Mortar Exposed to Elevated Temperatures"],"prefix":"10.12688","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0009-0009-5185-064X","authenticated-orcid":false,"given":"Murtatha","family":"Alshijlawi","sequence":"first","affiliation":[{"name":"Anbar Technical Institute Baghdad Baghdad Governorate Middle Technical University"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7265-583X","authenticated-orcid":false,"given":"Sheelan","family":"Mahmoud Hama","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering Ramadi Al Anbar Governorate University of Anbar"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Musab A.","family":"Abdulhamed","sequence":"additional","affiliation":[{"name":"Anbar Technical Institute Baghdad Baghdad Governorate Middle Technical University"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ibraheem A","family":"Aidan","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering Ramadi Anbar University of Al Maarif"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Noor A","family":"Rajab","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering Ramadi Al Anbar Governorate University of Anbar"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-8814-9738","authenticated-orcid":false,"given":"Aymen","family":"Hameed  Fayyadh","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering Ramadi Al Anbar Governorate University of Anbar"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"2560","published-online":{"date-parts":[[2026,3,19]]},"reference":[{"key":"ref1","doi-asserted-by":"publisher","first-page":"22226-22231","DOI":"10.48084\/etasr.10283","article-title":"Flexural Characteristics of Hollow One Way-Ferrocement Slabs.","volume":"15","author":"B Ismael","year":"2025","journal-title":"Eng. 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Absence of Microstructural Evidence:&nbsp;<\/b>The paper's main mechanistic claim \u2014 that melting PP fibers form micro-channels that reduce internal vapor pressure and prevent explosive spalling \u2014 is reiterated throughout the results and discussion but lacks direct evidence. No SEM images are included, making this key assertion speculative. To support this, SEM images of fractured mortar cross-sections after exposure to 200&deg;C, 400&deg;C, and 600&deg;C should be provided for both the control and fiber-reinforced mixes, with annotations highlighting micro-channel formation, fiber remnants, the fiber\u2013matrix interface, and void distribution. Additionally, quantitative porosity measurements via Mercury Intrusion Porosimetry (MIP) or Ultrasonic Pulse Velocity (UPV) testing would strengthen the existing density and strength data. \n<b>Response to reviewer comment:<\/b> While Scanning Electron Microscopy (SEM) observations would indeed provide direct microstructural visualization, SEM analysis was not performed in the present experimental program due to laboratory limitations. Nevertheless, in response to the reviewer\u2019s suggestion, Ultrasonic Pulse Velocity (UPV) testing has been conducted and incorporated into the revised manuscript to provide additional quantitative insight into the internal damage and microstructural deterioration of the mortar specimens after thermal exposure. A new subsection entitled \u201c3.7 Ultrasonic Pulse Velocity (UPV) Analysis\u201d has been added to the Results and Discussion section. The UPV results show a progressive reduction in wave velocity with increasing temperature and fiber content, which indicates the development of internal microcracks, pore expansion, and increased internal voids within the mortar matrix. These observations are consistent with the reductions observed in density and mechanical strength. The authors acknowledge that future work will include detailed microstructural characterization using SEM and pore structure analysis techniques such as Mercury Intrusion Porosimetry (MIP) to further investigate the micro-channel formation and pore evolution in heated mortar.  2. \n<b>Superplasticizer Characterization and Workability Methodology:&nbsp;<\/b>The manuscript mentions '1% superplasticizer type F' but does not specify the manufacturer, product name, code, or chemical base, which are necessary for reproducibility. More importantly, the superplasticizer dosage was kept constant across all mixes while PP fiber content varied from 0% to 1.5%. This caused a 32.4% reduction in flow diameter in the highest fiber mix, potentially affecting casting quality and confounding the interpretation of compressive strength at higher fiber levels. The lower strength might partly result from reduced workability rather than fiber effects alone. The authors should either (a) modify the superplasticizer dosage for each mix to ensure consistent workability before casting strength tests, or (b) clearly state this as a study limitation and estimate its possible influence on the results. \n<b>Response to reviewer comment:<\/b> The Materials section has been revised to clearly describe the type and technical properties of the superplasticizer used in this study. The manuscript now specifies that a polycarboxylate-based high-range water-reducing admixture, Sika ViscoCrete-180 GS, conforming to ASTM C494 Type F, was used. Additional information regarding its specific gravity (1.07), pH range (4\u20136), color (light brownish), and dosage (1% by weight of cement) has been added to improve the clarity and reproducibility of the experimental methodology. \u201cA polycarboxylate-based high-range water-reducing admixture (HRWR), Sika ViscoCrete-180 GS, conforming to ASTM C494 Type F, was used to improve the workability of the mortar mixtures. The superplasticizer has a specific gravity of approximately 1.07, pH value ranging from 4 to 6, and a light brownish liquid appearance. The admixture is based on modified polycarboxylate ether technology and was added at a constant dosage of 1% by weight of cement for all mixtures to maintain comparable workability conditions while isolating the effect of polypropylene fiber content on the fresh and hardened properties of the mortar.\u201d   3. \n<b>Missing Specimen Replication Details and Flexural Testing Setup:<\/b>&nbsp;The methodology lacks details on the number of specimens used for density measurements, and the overall specimen count for each property\u2013temperature\u2013fiber combination is not summarized. A table should be included, listing specimen counts, dimensions, and related test standards for each measured property. Furthermore, Section 2.2 does not clarify whether flexural testing was conducted under displacement or load control, nor does it specify the crosshead speed (mm\/min) or the model and capacity of the testing machine. Since toughness values are obtained from load\u2013deflection curves, knowing the testing rate is essential; without this, the toughness data cannot be independently verified or reproduced. \n<b>Response to reviewer comment: <\/b>A new summary table has also been added to the manuscript to clearly present the specimen count, specimen size, and relevant test standards used for density, compressive strength, flexural strength, and UPV measurements, see Table 2. Also, Section 2.2 has been expanded to clarify the flexural testing procedure and loading conditions. The manuscript now specifies that the flexural tests were performed using a three-point bending configuration on prism specimens (50 &times; 50 &times; 160 mm) in accordance with ASTM C348. The tests were conducted using a universal testing machine with a capacity of 300 kN, and the loading was applied under load control at a constant rate of 50 &plusmn; 10 N\/s, as specified in the standard. During testing, the load\u2013deflection response was recorded to evaluate post-cracking behavior and flexural toughness.    4. \n<b>PP Fiber Type and Internal Melting Temperature Inconsistency:<\/b>&nbsp;The fiber type (monofilament or fibrillated\/multifilament) and the manufacturer or product name are not specified. These details affect fiber\u2013matrix bonding, dispersion, and thermal properties, and should be included as standard information. Additionally, there is an inconsistency regarding the melting temperature: the abstract and Section 2.1 report a melting point of 160\u2013170&deg;C, whereas Section 3.4 states that PP fibers 'melt near 320\u2013340&deg;C'. This discrepancy needs clarification and resolution. The 160\u2013170&deg;C range corresponds to the standard melting point of isotactic polypropylene, while the higher temperature likely refers to a different thermal or kinetic condition. Consistent use of the correct values throughout the document is essential manuscript. \n<b>Response to reviewer comment: <\/b>The authors thank the reviewer for this important observation. In response to this comment, the manuscript has been revised to clarify both the type and manufacturer information of the polypropylene fibers and to resolve the inconsistency regarding the reported melting temperature. First, the fiber type has now been clearly specified in Section 2.1. The polypropylene fibers used in this study are monofilament polypropylene fibers with a length of 12 mm and a diameter of approximately 18 \u03bcm. These fibers were selected due to their effectiveness in improving crack resistance and reducing spalling in cementitious composites exposed to elevated temperatures. Second, the inconsistency related to the melting temperature has been corrected throughout the manuscript. The correct melting temperature of polypropylene fibers is approximately 160\u2013170&deg;C, which corresponds to the melting point of isotactic polypropylene reported in the literature. The previously stated value of 320\u2013340&deg;C in Section 3.4 was incorrect and has been removed from the revised manuscript to maintain consistency. The text in Section 3.4 has been revised accordingly to state that polypropylene fibers soften and melt at approximately 160\u2013170&deg;C, forming micro-channels within the cementitious matrix that facilitate vapor release and reduce internal pore pressure during heating. These revisions ensure consistency and improve the clarity and accuracy of the material description in the manuscript.  \n<b>5. Curing Conditions:<\/b>&nbsp;The manuscript states that curing occurred 'in water at 20 &plusmn; 2&deg;C until 28 days old,&quot; but it does not clarify whether the water was lime-saturated, which is the standard method to prevent calcium leaching from mortar and influences hydration products and final strength. Additionally, it is not mentioned if the curing water was renewed regularly. These details should be included. \n<b>Response to reviewer comment:<\/b> &nbsp;In the present study, the specimens were cured in tap water maintained at 20 &plusmn; 2&deg;C until the age of 28 days. Although lime-saturated water is sometimes recommended to minimize calcium leaching, the use of tap water for curing cementitious specimens is a common laboratory practice and has been widely adopted in many experimental studies on mortar and concrete. To maintain stable curing conditions, the curing water was periodically renewed, and the temperature of the curing tank was maintained within the specified range (20 &plusmn; 2&deg;C). These details have now been clarified in Section 2.1 of the revised manuscript to improve the transparency and reproducibility of the curing procedure.   6. \n<b>Novelty Justification and Literature Differentiation:<\/b>&nbsp;Although the mortar-vs-concrete distinction is presented as the novelty claim, the Introduction lacks a detailed mechanistic comparison to fully justify why this difference merits separate investigation. The literature should be cited to discuss the specific quantitative differences in paste-to-aggregate ratio, pore-size distribution, and thermal cracking mode between mortar and concrete. Additionally, in Sections 3.3 and 3.5, where results are compared with previous studies, it should be clearer whether those studies examined mortar or concrete. Each comparison ought to specify the material system used in the cited work and emphasize the mortar-specific findings of the current study. \n<b>Response to reviewer comment: <\/b>The novelty of this study lies in providing a comprehensive experimental evaluation of polypropylene fiber\u2013reinforced cement mortar exposed to elevated temperatures up to 600&deg;C. While most previous studies have focused primarily on fiber-reinforced concrete, the present work specifically investigates mortar systems, which exhibit different behavior mechanisms. In addition to conventional strength measurements, this study systematically examines residual compressive strength, flexural strength, load\u2013deflection behavior, and flexural toughness after thermal exposure. The work also identifies the best polypropylene fiber dosage for improving post-fire mechanical performance of mortar and provides detailed insights into the role of fiber melting in reducing thermal damage and enhancing residual structural integrity.   7. \n<b>Internal Inconsistency in Compressive Strength Reporting:<\/b>&nbsp;In Section 3.3, it states that mortars reinforced with PP fiber 'maintain a comparatively higher strength (33\u201328%, respectively)' for the 0.5% and 1.5% PP mixes at 600&deg;C. However, Table 3 shows the 1.0% PP mix retains 27.6%, and the 1.5% PP mix retains 26.5%. The 1.5% mix is not the pair being described. The text should be revised to accurately reflect the tabulated values for each mix separately and organize the performance ranking clearly. \n<b>Response to reviewer comment: <\/b>The authors appreciate the reviewer for carefully identifying this inconsistency in the description of the residual compressive strength results. The statement in Section 3.3 has been revised to accurately reflect the values reported in Table 3. According to the experimental results, at 600&deg;C, the residual compressive strength values were 33.4% for the 0.5% PP mix, 27.6% for the 1.0% PP mix, and 26.5% for the 1.5% PP mix, compared with 19.1% for the control mixture. Therefore, the 0.5% PP mixture exhibited the highest residual strength, followed by the 1.0% PP and 1.5% PP mixtures, respectively. The manuscript text has been corrected to clearly present this ranking and ensure consistency with Table 4.  8. Dedicated Limitations and Future Work Section:&nbsp;The manuscript lacks a 'Limitations and Future Work' section, which is a notable omission. The following limitations should be explicitly recognized: (a) only one PP fiber geometry was tested; comparing it with basalt, steel, or hybrid systems would enhance the applicability; (b) only a single mortar mix design (w\/c = 0.45, 1:3 cement to sand) was studied; (c) the highest temperature tested, 600&deg;C, does not encompass more extreme fire scenarios reaching 800\u20131000&deg;C; (d) long-term durability aspects such as carbonation, chloride resistance, and creep after thermal exposure were not evaluated; and (e) the influence of different cooling methods (furnace cooling versus water quenching) on residual properties was not addressed, although this is crucial for post-fire structural assessments. \n<b>Response to reviewer comment:<\/b>\n<b> <\/b>\n<b>&nbsp;<\/b>The authors appreciate this valuable suggestion. Accordingly, a short \u201cLimitations and Future Work\u201d statement has been incorporated in the revised manuscript. The present study is limited to a single PP fiber geometry and one mortar mix design (w\/c = 0.45; cement:sand = 1:3) with a maximum exposure temperature of 600&deg;C under furnace cooling conditions. In addition, long-term durability aspects after thermal exposure were not examined. Future research will investigate alternative fiber systems (e.g., basalt, steel, or hybrid fibers), higher fire temperatures (800\u20131000&deg;C), different cooling regimes, and microstructural characterization techniques (e.g., SEM and porosity analysis) to provide deeper insight into thermal damage mechanisms.    \n<b>9. Minor Typographical and Presentation Errors:<\/b>&nbsp;Several typographical and presentation errors need correction. The axis label 'Temretures, 0C' in Figures 5, 6, and 9 should be amended to 'Temperature (&deg;C)'. The term 'formulation' in Section 3.5 should be changed to 'formation' ('pore formation'). The phrase 'control mia' in Section 3.4 should be corrected to 'control mix'. The label 'pp%' in Figure 4 should be standardized as 'PP fiber content (%)'. Lastly, Figure 10 (toughness) would be improved by adding a supplementary data table similar to Tables 2\u20135, enabling readers to easily access the exact numerical toughness values. \n<b>Response to reviewer comment:<\/b> The authors thank the reviewer for carefully identifying these typographical and presentation issues. Also, Table 7. Flexural toughness and percentage change relative to the control mix (0% PP) at each temperature, has been added","URL":"https:\/\/f1000research.com\/articles\/15-30\/v2#referee-comment-15587","order":2,"name":"referee-comment-15587","label":"Referee Comment","group":{"name":"article-reports","label":"Article Reports"}},{"value":"10.5256\/f1000research.197465.r497918, Aktham Hatem Qasim, University of Fallujah, Fallujah, 28 Jul 2026, version 2, indexed","URL":"https:\/\/f1000research.com\/articles\/15-30\/v2#referee-response-497918","order":3,"name":"referee-response-497918","label":"Referee Report","group":{"name":"article-reports","label":"Article Reports"}},{"value":"The author(s) declared that no grants were involved in supporting this work","order":4,"name":"grant-information","label":"Grant Information"},{"value":"This is an open access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.","order":0,"name":"copyright-info","label":"Copyright"}]}}