Properties of Hardened Concrete Produced by Waste Marble Powder

AbstractMarble is industrially processed by being cut, polished, and used for decorative purposes, and thus, economically valuable. In marble quarries, stones are cut as blocks through different methods. During the cutting process, 20-30% of a marble block becomes waste marble powder. Marble powder is a waste material generated in considerable amounts in the world. Marble waste leads to a serious environmental problem as well. Therefore, the use of waste marble in the concrete production as an admixture material or aggregate has increasingly become an important issue. In the present study, effect of different usage areas of waste marble on the hardened concrete properties was investigated based on previous studies. In this context, (1) compressive, flexural, and splitting tensile strength, (2) modulus of elasticity, (3) ultrasonic pulse velocity, (4) Schmidt surface hardness, and lastly (5) sorptivity coefficient/porosity of the hardened concrete, were examined. Comparing all results, the proposition “the marble waste can be used in the production of concrete” was discussed in a detailed manner. As a result, the use of waste marble powder in (1) conventional concrete mix, (2) self-compacting concrete mix, and (3) polymer concrete mix, was revealed. Consequently, it was found out that the use of waste marble in the conventional concrete mix as an admixture material or aggregate is suitable as it can improve some properties of the hardened concrete. However, the use of waste marble in the self-compacting and polymer concrete mixes as an admixture material or aggregate is not affected positively in terms of hardened properties of concrete

Fuzzy multi-criteria decision making model for subcontractor selection in international construction projects

A general contractor’s ability to select proper subcontractors in foreign projects is a key competitive advantage. Toward this aim, a subcontractor selection model (CoSMo) was developed in this study. As a computational approach, the fuzzy sets method was employed because it can model human judgment by means of linguistic values, combining qualitative and quantitative decision criteria into an aggregate measure. Although the algorithm may be complex for easy acceptance by industrial practitioners, this disadvantage was minimized through a computer-supported system. In order to gain a better understanding of the current practice of CoSMo, a real world construction project was conducted. As a result, it was observed that CoSMo has high practical application and can be used as an advisory system by satisfying principal contractor’s requirements to reduce the risk involved in the selection of a subcontractor. Moreover, it gives an initial idea of how subcontractors perform on each decision criterion and allows the main contractor to understand the picture on the strong and weak points of each bidder and thereby to take conscious decisions. First published online: 10 Jun 201

A multiple criteria decision‐making approach to the selection of concrete pumps

In this study, the ELECTRE III method, which is one of the most common techniques among multiple criteria decision‐making (MCDM) approaches, was considered in a selection problem of concrete pumps. As a methodological framework, a two‐step questionnaire survey was conducted by 70 firms that have and use concrete pumps. A solution of the problem was then found in the light of the real world data by means of ELECTRE III. The paper can be of value to researchers studying the anatomy of decision‐making in equipment selection in general and investigating selection criteria of concrete pumps in particular. It also contributes to the academic environment as an application practice of ELECTRE III to correspond with the nature of equipment selection and as an effective means for the formalization of knowledge possessed by industrial practitioners. On the practical side, ELECTRE III offers an efficient and convenient tool that forces the users into orderly and methodical thinking, and guides them in making logical and robust decisions. In addition, the example illustrated in the present study can be helpful for decision‐makers dealing with similar equipment selection issues. Santrauka Šio tyrimo ELECTRE III metodas – vienas dažniausiai taikomų metodų iš daugiatikslių sprendimo priėmimo metodų – buvo pritaikytas betono siurblių parinkimo uždaviniui spręsti. 70 įmonių buvo apklaustos dviem etapais. Tuomet buvo išspręstas realus uždavinys realiais duomenimis, taikant ELECTRE III metodą. Straipsnis gali būti naudingas tyrėjams, nagrinėjantiems įrenginių parinkimo uždavinių prigimtį ir esmę. Šis straipsnis turi akademinę ir praktinę vertę, nes išreiškia efektyvių sprendimų priėmimo proceso esmę ir pateikia tvirtą sprendimo priėmimo pagrindą. Pateiktas praktinio uždavinio sprendimas yra gera metodinė priemonė parenkant statybinius mechanizmus. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: betono siurblys, statybinis įrengimas, ELECTRE III, daugiatikslis sprendimų priėmimas, parinkimas

A structured selection process for small and medium enterprises in construction industry: Case of international projects

Construction industry in most countries relies heavily on small and medium enterprises (i.e., subcontractors). Therefore, in today’s highly competitive construction business, it is inevitable to select suitable subcontractors which physically execute almost all of production activities in construction projects. In this context, through a proper selection process, their competences should be guaranteed as much as possible. In fact, this becomes a more significant issue if the project undertaken is performed abroad. In this regard, it should be noted that Turkish construction companies have been significantly active in the international arena for decades. Based on these arguments, subcontractor characteristics to be considered in international projects should be revealed clearly. Accordingly, this paper proposes a structured process for subcontractor selection in international construction projects. Toward this aim, a questionnaire survey was applied to 96 construction companies, all of which are members of Turkish Contractors Association, and the corresponding numerical results were evaluated via descriptive statistics and 95% confidence interval. Thus, a three-step selection procedure together with their specific criteria was suggested from the conceptual point of view. These steps include (i) shortlisting with ten criteria, (ii) negotiation with seven criteria, and lastly (iii) final selection with seven criteria. Hence, this study can provoke potential researchers to find similarities or differences of such criteria between their countries and Turkey. Also, it can help both main contractors to execute the whole construction process in a financially sustainable environment and subcontractors to increase business opportunities in the international market

Comparative life cycle costing analysis of green roofs: The regional aspect

The increasing environmental concerns and poor practices force construction industry to take some remedial measures for green and sustainable built environment. Especially in urban areas, one of these measures is to build green roofs for minimizing the environmental pollution. In fact, green roofs present a number of economic, environmental, and social benefits. However, compared with traditional roofs, green roof investments have high capital and maintenance costs and this makes potential investors hesitant about their applications. Therefore, in the present study, benefits and life cycle costing parameters of green roofs were evaluated through a literature review. In this context, numerical inputs and findings of past studies were utilized. In doing this, a special emphasis was placed on the regional characteristic of such investments as it is a natural feature of any life cycle costing analysis. In conclusion, the majority of benefits and life cycle costing parameters was found to be highly variable, and thus, any life cycle costing assessment that will be performed in the future should be case-sensitive instead of using some generalized or raw data. Therefore, based on findings and results of this study, industrial practitioners and potential customers may have a useful source of economic, environmental, and social information about green roofs while researchers may be encouraged for more region-specific studies

Subcontractor selection practices in international construction projects

This paper presents a study of subcontractor selection practices of Turkish contractors in international projects. The results highlight the current subcontracting practices of main contracting firms that have resulted in a long‐lasting market share abroad. Toward this aim, a detailed questionnaire was administered to 96 construction companies. Turkish and host countries’ subcontractors were shown to be frequently employed in international projects. However, subcontracting firms from other countries were found to not be used. Main contracting companies generally select subcontractors in the periods after the main tender or after the project's start. Although many of them often work with previously known subcontracting companies and do not take into account the lowest bid price as the primary criterion, systematic processes or models are not used to select the best subcontractor. Most importantly, main contractors not only use subcontractors but also carry out activities using their in‐house resources. Hence, this study will not only be a step for further works that can be performed by potential researchers who may find interesting similarities or differences between their countries and Turkey, but also assist contractors who plan to strengthen their positions and to increase work opportunities in the international market. Santrauka Straipsnyje pateikiami Turkijos generaliniu rangovu praktiniai subrangovu parinkimo tyrimai, vykdant tarptautinius pro‐jektus. Akcentuojama dabartine generalinio rangovo imoniu subrangos praktika, kuri sudaro ilgalaike ir plačia rinkos dali. Šiam tikslui buvo išsamiai apklausta iki 96 statybos imoniu. Turkijos ir kitu vadovaujančiaja pozicija užimančiu šaliu subrangovai teige, kad dažnai dirba su tarptautiniais projektais. Tačiau kitu šaliu subrangos imones nedalyvauja toje veik‐loje. Generalines rangovo imones paprastai pasirenka subrangovus pateikus pagrindini pasiūlyma arba projekto pradžioje. Nors daugelis iš ju dažnai dirba su jau anksčiau žinomomis subrangos imonemis ir pasirinkdamos geriausia subrangova neatsižvelgia i pagrindini rodikli‐ žemiausia siūloma kaina, nenaudoja sisteminiu procesu ar modeliu. Svarbiausia, kad generaliniai rangovai naudojasi ne tik subrangovu paslaugomis, bet ir vykdo veikla, naudodamiesi ju turimais vidaus ištekliais. Taigi šis tyrimas bus ne tik potencialiu tyreju žingsnis igyvendinti ir rasti idomiu panašumu bei skirtumu tarp šiu šaliu ir Turkijos, bet ir padeti rangovams stiprinti savo pozicijas bei didinti isidarbinimo galimybes tarptautineje rin‐koje. First Publish Online: 15 Oct 2010 Reikšminiai žodžiai: subrangovai, parinkimas, užsienio projektai, statybos imone

Causes of delays in construction projects in Turkey

In both developing and industrialized countries, deviation from a planned time schedule is one of the most frequently encountered problems in construction investments. Various factors faced with during construction period prevent systematic flow of work, which causes time-based anomalies as a conclusion. Considering the vital importance of the construction industry on the macro-economic structure of a country, it is inevitable to be aware of considerable effect of the timely completion on the allocated project budget. In this study, causes of time extensions in the Turkish construction industry and levels of their importance were examined together. In total, 34 factors affecting project duration were taken into account. A questionnaire survey, including these factors, was then applied to 71 construction companies in Turkey, and the outcomes were evaluated by means of statistical analyses. According to the results, “design and material changes” was found to be the most predominant factor, followed by “delay of payments” and “cash flow problems”. In terms of importance levels of factor groups, financial factors were found to be the first group, while environmental factors were the least effective group. It should be also noted that managerial causes of time extensions are encountered in developed and developing countries, whereas financial causes are experienced in developing countries only

Ceramic wastes usage as alternative aggregate in mortar and concrete

In the ceramic industry, huge amounts of wastes are generated during manufacturing and transportation processes. In order to decrease the need for landfill areas and increase environmentally harmful effects of such wastes, this industry is under pressure to finding effective ways for recycling its wastes and by-products. In addition, the construction industry requires new sources of aggregates due to running out of conventional virgin aggregates, saving energy, and protecting the environment. Therefore, recently, ceramic wastes are often used as coarse and/or fine aggregate both in mortar and concrete. In the present study, effects of using ceramic wastes as coarse and/or fine aggregate on the engineering properties of mortar and concrete are evaluated. These engineering properties are listed and compared according to their mechanical and durability properties. Reviewing of previous studies related with this subject in literature and discussion all results of the studies are conducted as the methodology of this study. Consequently, it was found out that the use of waste ceramic in the conventional concrete or mortar mix as fine/coarse aggregate is suitable as it can improve mechanical and durability properties of the concrete/mortar

Building bridges: toward alternative theory of sustainable supply chain management

We contend that the development of sustainable supply chain management (SSCM) theory has been impaired by a lack of paradigmatic dive rsityin the field. The contested nature of the concept of sustainability has been repressed in SSCM theory, which has led to SSCM cutting itself off from debates that could be the source of inspiration for the development of interesting theory. We adopt the problematization approach proposed by Alvesson and Sandberg (2011) in order to unveil some of SSCM’s unquestioned assumptions, propose an alternative assumption ground, and in this way move toward stronger theory in SSCM. We use paradoxical framing to make sense of the inherent tensions between the different levels of sustainability and between the different types of theory being produced in response to the challenges of sustainability. We articulate a number of foundational assumptions for an alternative theory of SSCM that emerge from the various tensions identified between the different paradigms of sustainability. Finally, we identify a number of ideas for future research that would enable researchers to empirically explore the alternative assumptions