1- Introduction

2- Geopolymerization

3- Review of literature

4- Conclusion

References

Abstract

The utmost priority in reducing the usage of ordinary Portland cement (OPC) while replicating the cementitious properties by utilizing industrial by-products in construction materials is seriously undertaken by many researchers. The technology of geopolymerization that utilizes materials and activator solution to form geopolymer matrix could lead to alleviate some of the issues related to OPC based concrete. Numerous experiments have established that geopolymer concrete has higher compressive strength, higher acid resistivity and lower shrinkage than ordinary concrete. This review article focusses on the microstructure analyses of the geopolymer specimens and comparison of geopolymers with various binders. The review analysis of various binders used and their microstructural investigations reveal that different molarity of sodium hydroxide or phosphoric acid solution, liquid-to-binder ratio, curing temperature and duration yield geopolymers of diverse properties. Most of the geopolymer products revealed a wide hump in the XRD analysis due to the amorphous structure of aluminosilicate. Investigation of MIP and Micro CT reveals that aged geopolymer has a denser matrix arrangement and produce high compressive strength. Geopolymerization prevents interconnectivity of micropores due to the formation of denser matrix of geopolymer gel. Generally, the use of 12M of sodium hydroxide solution, low liquid-to-binder ratio of about 0.4 and curing temperature at approximately 70 °C for at least 24 h produced high strength geopolymers. The binders mixed with lower sodium silicate to sodium hydroxide mass ratio of 2.0–2.5 tend to react more efficiently.

Introduction

It is well known that limestone hills were being harvested for cement manufacturing throughout the world and that lead to ecological imbalance [1]. As concrete is the most widely used construction material, the exploitation of natural resources such as sand and coarse aggregate pressured construction industry to look for alternatives for these materials; thus, the use of alternative construction materials is on the rise and many research works are being carried out through the globe. Cement manufacturers rely on limestone as it is the major source in ordinary Portland cement. For the conversion of limestone to calcium oxide, the cement kiln heats all the raw materials at high temperature. Fuel used in heating may be coal, natural gas, sawdust and methane gas or a combination of these fuels. Both the chemical conversion and firing process release carbon dioxide (CO2), which is the main component in greenhouse gas. Alnahhal et al. [2] reported that about 2.8 billion tonnes of cement products manufactured every year and this in turn produces about 5–7% of the global CO2 emissions [3,4]. Based on a report by Department of Statistic Malaysia, roughly 20 Mega tonnes of cement were produced in 2016 [5]. It has been reported that the production of cement, besides consuming the natural resources, it also destroys the natural habitat of flora and fauna [1]. Since the beginning of 1990s, the term sustainability has gained significance among all engineering community and more focused works are being systematically carried out throughout the globe in diverse areas of engineering process and products. Thus, more researches have been carried out in the area of building materials, especially on cement-based products by using diverse cement replacement materials which fulfill both the sustainability criterion to conserve the natural resources and preserve the environment.

مقاله کنونی، روشهای مختلف برای ناپیوستگی و براورد قالب سنگ را مورد نقد و بررسی قرار میدهد. انواع تکنیکها برای تعیین شکل و توزیع اندازه قالبسنگها، به روشهای شاخص و مدلسازی، تقسیم شد. روشهای شاخص، اندازه متوسط قالبسنگ را به صورت یک معرف توده سنگ محاسبه میکند. این روشها، ساده، ارزان و سریع هستند، اما به خطاهای بزرگ به خاطر وجود توده ی سنگ قالبسنگها وابسته میباشند. از اینرو، روشهای شاخص، توصیه نمیشوند. در تکنیکهای مدلسازی، براوردهای ناپیوستگی سعی دارند توده سنگ را به طور واقع گرایانه برای تعیین هندسه ی کل بلوک ها با لگاریتم های مختلف مدلسازی کنند. این روشها، هم چنین دارای نواقصی در مدلسازی ناپیوستگی ها و محاسبه هندسه بلوک ها هستند. برای انجام ارزیابی کل روشها، شش شرط برای تعیین روش برای براورد قالبسنگها شناسایی شد. این شرایط عبارتند از: توانایی مدلسازی ناپیوستگی های تصادفی و مجموعه های مشترک با ابعاد ویژه، ناتوانی شبیه سازی ناپیوستگی ها با روشهای آماری (توانایی مطالعه یک شبکه ناپیوستگی به طور مجزا)، تعیین هندسه کل قالبسنگها، بررسی ناپیوستگی های آویزان و مجزا، سادگی و سه بعدی بودن. بر مبنای شرایط لازم فوق، یک رویکرد جدید برای تعیین روشهای مناسب در ارزیابی سنگهای بریده ارائه شده است. این متدولوژی جدید در معدن سنگ آهک در جوشغان، ایران برای تحقیق در مورد کاربردپذیری روشهای مختلف در معادن سنگ بریده، بکار رفته است.