International Conference on Sustainable Design, Engineering and Construction

Investigation of Concrete Recycling in the U.S. Construction Industry

Ruoyu Jina, Qian Chenb

aUniversity of Nottingham Ningbo China, 199 TaikangEast Rd. Ningbo 315100, China

bThe Ohio State University, Columbus, 43210. U.S.A.

Abstract

The emerging sustainable development movement in the construction industry requires the recycling of waste materials to reduce the negative environmental impact of construction activities. In many countries, old concrete, a major waste stream generated from the demolition of obsolete buildings/structures, is being recycled. However, for various reasons, progress toward concrete recycling varies from country to country. This paper discusses the current status of concrete recycling in the U.S. construction industry based on results from a two-part questionnaire survey. The first part of the survey collects information on the recycling practices of surveyed concrete companies. The second part adapts questions from a study conducted in Australia and Japan to examine the awareness, benefits, difficulties, and recommended methods related to concrete recycling. The findings showed that although recycling old concrete is common in the U.S., its application is mostly limited to backfill and pavement base; using waste concrete in new concrete production is not widely applied. There are also similarities and differences in the perceptions of concrete recycling between U.S. concrete companies and their counterparts in Australia and Japan.

© 2015 The Authors. Published by Elsevier Ltd.

Peer-review under responsibility of organizing committee of the International Conference on Sustainable Design, Engineering and Construction 2015.

Keywords: Waste Concrete; Concrete Recycling; Demolition; United States; Australia; Japan

Introduction

The wide use of concrete in construction has raised multiple environmental concerns due to its high usage of raw materials, the high energy consumption of cement manufacturing, transportation, and the creation of large volumes of old concrete from demolition wastes [1]. It was estimated that the concrete industry uses approximately 10 billion tons of sand and natural rock worldwide, and simultaneously over 11 billion tons of construction and demolition (C&D) waste are produced annually [2]. Concrete waste accounts for about 50% of the total construction waste [3]. Other studies even disclosed a higher percentage (i.e., 70%) of concrete in the construction waste [4]. On the other hand, cement manufacturing is very energy-intensive. It was estimated that at least 3.79 million Btus of energy is needed to produce each ton of cement. This level of consumption leads to high greenhouse gas emissions (e.g., accounting for 7% of CO2 emissions globally) by the cement industry [5].

In recent years, environmental consciousness, protection of natural resources, and sustainable development have become significant factors in modern requirements for the construction industry worldwide [1]. Recycling of old concrete is one of the main approaches to meeting these requirements. However, recycling of old concrete faces various difficulties such as the inferior quality of recycled aggregates and increased labor cost [1,6]. At the current stage, not much direct assistance is given to practitioners to help them address potential challenges encountered in the concrete recycling process, except for a few scattered efforts (e.g., [7]). In general, there is a lack of comprehensive understanding on the current status of concrete recycling and related barriers, based on which effective coping strategies could be developed.

This study aims to explore the current status of concrete recycling in the U.S. construction industry through a two-part questionnaire survey. The first part of the survey collects information regarding the current practices of concrete recycling in the U.S. The second part adapts questions about the awareness, benefits, difficulties, and recommended methods related to concrete recycling from a similar study [8] performed in Australia and Japan. This enables an international comparison of the current stages of concrete recycling practice. The similarities and differences in light of the perceptions of concrete recycling between the U.S. and the other two countries are also discussed.

Literature review of concrete recycling

Benefits to recycling waste concrete

Concrete is the most widely used building material in the world [9]. Consequently, concrete waste is one of the major waste streams in C&D debris. Recycling and reapplying waste concrete has apparent environmental benefits, as well as many other advantages. First, recycling concrete wastes as aggregates (i.e. RCA) reduces the amount of waste and preserves natural resources [10]. This can reduce the growing pressure on landfill capacity as waste concrete amounts from construction and demolition increase [11]. Second, using RCA reduces greenhouse gas emissions associated with concrete production using virgin aggregates [12]. The use of RCA also carries economic advantages and aids in regulatory compliance. Manufactured RCA has become more economical than virgin aggregate in terms of transportation costs and the increased cost of landfilling C&D debris [13]. In addition, government authorities in Europe, Japan and the U.S. have begun to encourage the usage of RCA either through direct demands or indirectly (e.g., increasing tipping fees for landfilling concrete wastes).

Progresses in concrete recycling

Old concrete can be recycled into aggregates and used in many civil engineering applications, including road pavement materials, sub-basements, soil stabilization, and production of new concrete [1]. However, progress toward concrete recycling may vary in different countries for various reasons. These include the availability of technical specifications, recycling technologies, and the level of government support.

An early estimate [14] revealed that up to 1998, more than half of cement concrete debris generated in the U.S. ended up in landfills. Of all recycled cement concrete debris, 85% was used as road base. They further indicated that RCA was being increasingly used to replace natural aggregate in various other road construction applications such as concrete mix and top-course asphalt. It was found out that the lower transportation cost of processed waste concrete aggregates might have been the incentive that promoted the use of RCA in the U.S [15]. However, most of the waste aggregates were only suitable as backfill or construction base.

Difficulties Encountered in Concrete Recycling

Cost and energy consumption are two of the key issues considered in adopting the concrete recycling approach. A case study was conducted in Australia [3] to compare cost and benefits between 1) dumping waste concrete in a landfill and producing natural materials for new concrete and 2) recycling old concrete as aggregates for new concrete. The latter approach was found to be cost-effective while also protecting the environment and achieving construction sustainability. In contrast, the labor cost incurred in the extraction of waste aggregates from demolished buildings and the cost of using admixture to increase the strength of concrete using waste aggregates compared to the cost of natural aggregates was concerned [6]. Another concern lies in the quality of products made of RCA. The source of old concrete was usually unknown [1]. Additionally, the use of RCA should be restricted due to the different properties of RCA compared to virgin aggregates. For example, it was found that RCA concrete requires a lower water/cement ratio and higher cement content to achieve a strength comparable to conventional concrete [7]. [13] revealed RCA’s negative effects on concrete production and properties. In [16], the key concerns about concrete recycling were economy, policies and strategies, certification of recycled materials, planning of demolition projects, and most importantly, education and information.

Research Methodology

This study aimed to explore the current status of concrete recycling in the U.S. construction industry. It has three specific objectives, as listed below:

To obtain background information on U.S. concrete recycling practices, including the source of concrete waste, ways of handling old concrete in the field, application of recycled concrete, etc.;

To acquire industry practitioners’ perceptions of current concrete recycling practices in terms of awareness, benefits, difficulties, and potential strategies; and

To compare the results of this study with a previous study that investigates concrete recycling in other countries, including the leading country: Japan.

A questionnaire was developed for face-to-face interviews and an online survey. Concrete companies in Central Ohio were identified for face-to-face interviews through two public sources: the 2008 Membership Directory of Builders Exchange of Central Ohio and the 2012 Directory of Ohio Ready Mixed Concrete Association (ORMCA). Participants for the online surveys were found from ORMCA and the C&D facility list from the California Department of Resources Recycling and Recovery. Companies were asked to have their most knowledgeable or experienced people take the survey, if possible.

The questionnaire consisted of two parts. Part One was designed to collect the background of survey participants. Multiple-choice and open-ended questions were used to learn about the surveyed individuals’ experience in the concrete industry, their companies’ role in concrete recycling, the size of their companies, and other information regarding their companies’ engagement in concrete recycling. Part Two was adapted from a similar study [8] that investigated and compared the concrete recycling practices of Australian and Japanese construction industries. This part of the questionnaire was divided into four sections: Awareness, Benefits, Difficulties, and Recommended Methods for Concrete Recycling. In the “Awareness” section, multiple-choice questions were used, which featured three options: “Yes,” “No,” or “Have no idea.” Questions in the other three sections were all based on the Likert scale format. Specifically, five options from “1” to “5” were available for each given statement, with “1” denoting “least important” or “strongly disagree,” “3” indicating “neutral,” and “5” meaning “most important” or “strongly agree.” “N/A” (not applicable) was also provided for cases where the survey participants were not sure about a given statement. The responses of “Have no idea” or “N/A” were excluded in the final data analysis.

The developed questionnaire was expert reviewed by two representatives: one from the Builders Exchange of Central Ohio and the other from ORMCA. The questions taken from the survey in [8] were adjusted and some were removed based on the feedback received. This ensured that all questions asked were relevant to the U.S. concrete industry. The finalized questionnaire and survey/interview procedures were reviewed and approved by the University Institutional Review Board. The survey was conducted between July and October, 2012. To protect the confidentiality of survey participants and their companies, no identifiable information was saved in the survey process.

In addition to summarizing the background information collected through Part One of the questionnaire, this study adopted various statistical methods to analyze the information collected through Part Two. The results from Part Two were then compared to the findings from [8]. First, a two-tailed statistical analysis concerning two proportions [17] was used to analyze the awareness questions, for which a paired comparison was made on the percentage of positive answers to each question between this U.S. survey and the earlier surveys in Australia and Japan. The null hypothesis was that no significant difference existed in the given survey question between the two compared groups, based on the 5% level of significance. A p value of less than 0.05 would disprove the null hypothesis and lead to an alternative hypothesis that significant difference existed between the two compared groups, and the group with a higher percentage of positive answers would have a greater awareness for that given question.

Multiple statistical methods were used to analyze the Likert scale questions presented in other three sections. These methods are briefly described below:

The two-tailed statistical test concerning the difference between two means [17] is similar to the test concerning the two proportions mentioned above, with identical null and alternative hypotheses. The only difference is that the test compares two mean values generated from the Likert scale questions instead of two percentages.

Results and discussions

During the four-month study period, eight local concrete companies were interviewed by the researchers. Of 155 survey invitations sent out through emails, 17 companies responded and completed the online survey. This represented a response rate of 11%. In this study, the questionnaires collected through face-to-face interviews and online surveys were combined for data analysis. The results are presented and discussed in the following five subsections.

Background of survey participants

The background information collected included: 1) companies’ specific roles (e.g., demolition or recycling) in the concrete construction industry, 2) companies’ years in business, 3) surveyed individuals’ years of experience, 4) company size (i.e., number of full-time employees), 5) construction industry sectors involved (buildings, roadways/bridges, or others), 6) whether a company has received inquiries about concrete recycling, and 7) how a company handles concrete waste in its projects.

Figure. 1 shows the distribution of companies’ roles and sectors they served. When responding to these questions, survey participants were allowed to select more than one option that applied. It was found that more than half of the surveyed companies identified themselves as a recycler/hauler. Other roles mentioned were government, building materials, construction waste management consultant, etc. The survey results also showed that the same percentage (50%) of survey participants served in the building and roadway/bridge sectors. Some other sectors mentioned included recycling, demolishing, sorting procedure in landfills, and aggregates only.

Figure. 1. Company type distribution of survey participants

Survey participants were asked some general questions about their current and past practices in concrete recycling. The results are illustrated in Figure. 2. In terms of the source for potentially recyclable concrete, demolition of old structures was selected by 86% of survey participants, followed by 32% choosing “waste from site tests or leftover from pumping, over-order, and design change.” Other waste concrete (mentioned by 40% of respondents) came from infrastructure work, such as concrete roadways, bridges, airports, curbs, sidewalks, barriers, parking lots, and dams. When asked how their companies dealt with waste concrete that could potentially be recycled, 91% of respondents selected “recycled” while only 14% selected “disposed to landfill.” Respondents who selected “others” for this question specified that they reused the waste concrete as aggregate in road base or for resale. To the researchers, this was also one form of concrete recycling. Therefore, the survey results indicated a high concrete recycling rate among surveyed companies. Noticeably, some respondents chose both recycling and disposing as their ways to handle potentially recyclable concrete, indicating that they only recycled portions of the waste concrete materials and sent the rest to landfill.

Figure. 2. Past and current practice in concrete recycling of surveyed companies

In the subsequent question, survey participants were asked the typical range of concrete waste that was recycled in their previous projects. The given options were 0-25%, 25-50%, 50-75%, above 75%, or other percentage to be specified. While two and four respondents picked 0-25% and 25-50%, respectively, the majority of respondents (15 out of 21, or 71%) selected “above 75%.” Of these 15 respondents, four specifically stated that they had 100% waste concrete recycled. The combined recycling rate seems slightly higher than the estimated 50-60% in [14] and [18]. This could be due to the trend of increased concrete recycling rate in recent years. The survey also found that up to 90% of respondents had received inquiries about concrete recycling, showing the increased awareness among their clients.

When asked what recycled concrete was used for, the majority of respondents (77%) selected “backfill/roadbase.” Only 23% selected “aggregate for producing new concrete.” Other applications that were selected included aggregate filling, sub-base, roadway and building pads, base rock, drain rock, sand, and so on. One local respondent mentioned the use of RCA for non-structural walls and driveways in residential buildings. Survey participants were also asked to estimate the percentage of each application. The backfill/roadbase usage ranged from 20 to 100% with an average value of 70%. The percentage applied to the production of new concrete varied from 5 to 95%, with an average value of 30%. The survey results from the first part of the questionnaire concluded that most waste concrete in the U.S. was recycled and the most common application was backfill or roadbase.

Awareness of concrete recycling

The “Awareness” section in Part Two of the questionnaire consisted of six questions. Companies were asked about their policies for recycling, recycling methods used, the existence of a recycling department/division, employee training, etc. Table 1 displays the survey results and the comparison between the results of this study and Tam’s study [8] based on the two-tailed statistical analysis concerning two proportions.

As shown in Table 1, the 23 U.S. companies surveyed had high awareness regarding four awareness items, with positive answers ranging from 74% to 95%. These items were: A1) Having concrete recycling policies, goals, and procedures, A2) Having implemented one or more concrete recycling methods, A5) Planning to invest more resources in concrete recycling, and A6) Having handled waste concrete as recyclable material. Compared to their Australian counterparts, statistically higher percentages of U.S. survey participants had answered “Yes” to these four awareness questions. Item A4) Employees participate in training or program(s) regarding concrete recycling, received the lowest percentages of positive answers for both U.S. and Australian survey participants.

Table 1. Comparison of awareness survey results between the U.S., Australia, and Japan

Awareness	Test item	Results
U.S. (U) This study (N=23)	Australia (A) [8] (N=54)	Japan (J) [8] (N=80)
Yes	No	Yes	No	Yes	No
A1. Company has policies, goals and procedures for concrete recycling.	%	85%	15%	48%	52%	68%	32%
z	2.86(U/Aa)	2.32(A/Ja)	1.50(U/Ja)
p	0.005b(U/A)	0.022b(A/J)	0.136(U/J)
A2. Company has implemented one or more concrete recycling methods to achieve the stated policy or other requirements (e.g., LEED).	%	90%	10%	63%	37%	81%	19%
z	2.26(U/A)	2.32(A/J)	0.95(U/J)
p	0.027b(U/A)	0.022b(A/J)	0.342(U/J)
A3. Company has a specific division/department for concrete recycling.	%	50%	50%	52%	48%	61%	39%
z	0.51(U/A)	1.03(A/J)	0.93(U/J)
p	0.875(U/A)	0.303(A/J)	0.356(U/J)
A4. Employees participate in training or program(s) regarding concrete recycling.	%	33%	67%	41%	59%	64%	36%
z	0.61(U/A)	2.62(A/J)	2.53(U/J)
p	0.543(U/A)	0.010b(A/J)	0.013b(U/J)
A5. Company is planning to invest more resources in concrete recycling.	%	74%	26%	44%	56%	35%	65%
z	2.23(U/A)	1.05(A/J)	3.07(U/J)
p	0.029b(U/A)	0.296(A/J)	0.003b U/J)
A6. Waste concrete in past projects has been handled as recyclable materials.	%	95%	5%	70%	30%	80%	20%
z	3.26(U/A)	2.87(A/J)	1.72(U/J)
p	0.002b(U/A)	0.005b(A/J)	0.088(U/J)

aThe statistical test compares the survey results between two selected countries. Specifically, “U/A,” “A/J,” and “U/J” denote comparisons between the U.S. and Australia, Australia and Japan, and the U.S. and Japan, respectively.

bDenotes a statistically significant difference between the two countries compared.

These comparison results could be due to the problems identified by [8]: In Australia the following elements were lacking: 1) standardized policies and classification systems for concrete recycling, 2) financial support from the government to reduce the cost of recycling, and 3) technical specifications to expand the application of recycled concrete to producing new concrete. Although the U.S. may not be significantly better than Australia in these aspects, the researchers did find some related standards and specifications in the U.S. for recycling concrete waste, e.g., the aforementioned ODOT standard.

Compared to their Japanese counterparts, a significantly lower percentage of U.S. survey participants (33% versus 64%) had employees participating in training or programs regarding concrete recycling. However, a significantly higher percentage of these companies (74% versus 35%) were planning to invest more resources in concrete recycling. This could be explained by the fact that Japan may have already invested a lot of resources in this area, resulting in well-developed technologies, equipment, and training programs. This assumption could be further supported by Japan’s 100% concrete recycling rate, as observed by [8]. In contrast, the U.S. companies might be still on their way to developing more advanced technologies, equipping contractors with proper equipment, and training more employees. All of these require additional resources.

Benefits gained in concrete recycling

Eight Likert scale questions were designed to learn the survey participants’ perception of the benefits of concrete recycling. These included saving landfill space, conserving natural resources, reducing costs, etc. The two-tailed statistical test concerning the difference between two means was used to compare the results between this study and Tam’s study. Due to the limited data in [8], the comparison was only made between the U.S. and a sample combining Australia and Japan, rather than between these three countries. The comparison results are shown in Table 2.

Table 2. Comparison of perceived benefits to concrete recycling between the U.S., Australia, and Japan

Benefits	U.S. This study (N=23)	Australia & Japan [8] (N=134)	Statistical test results
Mean	Std.	Mean	Std.	z	p
B1. Conserving landfill space and reducing the need for new landfills	4.32	1.21	3.65	0.95	1.92	0.057
B2. Saving natural materials	4.32	1.25	3.85	0.91	1.69	0.094
B3. Reducing project costs by using recycled materials	4.32	1.21	2.90	1.04	5.19	0.000a
B4. Reducing the cost of transportation (from sites to landfills) and tipping fees	3.91	1.38	3.13	1.01	2.54	0.012a
B5. Stimulating continuous improvement in concrete recycling	3.86	1.08	2.94	0.92	3.79	0.000a
B6. Raising concrete recycling awareness	4.09	1.15	3.44	1.02	2.50	0.014a
B7. Increasing overall business competitiveness and strategic business opportunities	3.90	1.18	2.98	1.09	3.37	0.001a
B8. Improving management and communication on concrete recycling information and commitmentb	3.71	1.10	3.05	0.95	2.61	0.010a

aDenotes p values lower than 0.05, which indicated the existence of significant differences between the compared countries.

bDenotes items that had significant differences between Japanese and Australian surveys from Tam’s study (2009).

Table 2 shows the high mean values (ranging from 3.71 to 4.32) of the benefits questions from the U.S. survey. These indicate that the respondents had very positive views of the benefits gained in concrete recycling. These mean values are constantly higher than those from the combined Australian and Japanese surveys. Among eight items, B1) Conserving landfill space, B2) Saving natural materials, and B3) Reducing project costs, were deemed most positively by U.S. survey participants. The Australian and Japanese survey participants had slightly different views. While they perceived B1) and B2) most positively, similar to their U.S. counterparts, they deemed B6) Raising concrete recycling awareness, as the third most positively perceived benefit to concrete recycling, rather than B3. It seemed that the concrete recycling option was not very cost-effective in Australia and Japan for some reason. Statistical analysis confirmed that the U.S. survey respondents had significantly more positive views of items B3, B4, B5, B6 and B7 (p values lower than 0.05) compared to the combined sample group of Australia and Japan. However, for item B8) Improving management and communication, it was not clear which country had the most positive view since a significant difference existed between Australian and Japanese survey respondents in Tam’s study.

Difficulties in concrete recycling

In total, 19 Likert scale questions were asked regarding the difficulties in concrete recycling. These questions were divided into four subcategories: high cost investment, management skills, issues related to recycled concrete products, and lack of support. The survey questions and results, and international comparison results are displayed in Table 3. It can be seen that in the U.S. survey, 10 out of 19 items had mean values lower than 3. These average values falling between scales 2 “disagree” and 3 “neutral” showed the disagreement of survey participants in perceiving these difficulties in concrete recycling. In other words, the U.S. survey participants did not consider these items barriers. In contrast, only 2 out of the total 19 items in the Australian and Japanese surveys had average values below 3, and the majority of these 19 items were considered actual difficulties faced in concrete recycling.

Table 3. Survey results of perceptions on difficulties in concrete recycling

Difficulties	U.S. This survey	Australia & Japan [8]	Statistical test results
Mean	Std	Mean	Std	z	p
High cost investment
D1. The industrial waste sorting procedure is costly	3.26	0.87	3.04	1.07	1.00	0.319
D2. Transportation is costly from sites to recycling plants	3.20	1.01	3.28	0.97	0.33	0.740
D3. Placing recycling machines (e.g., crushers) onsite is difficultb	3.32	0.89	3.63	0.13	1.52	0.132
D4. The cost of waste removal (haul away) of recyclable concrete is higher than that of normal concrete removal	2.68	1.42	3.66	3.65	2.16	0.032a
D5. Recycling concrete increases labor and management costsb	2.58	1.26	3.06	1.09	1.58	0.116
Management skills
D6. It is difficult to create a plan of action for recycling concrete on a specific projectb	2.40	1.35	3.19	1.04	2.51	0.013a
D7. Recycling of concrete increases workload, such as documentation, supervision, etc.	2.65	1.27	3.07	1.01	1.41	0.159
D8. Recycling of concrete changes the existing practice of company structure and policy	2.70	1.03	2.87	0.90	0.70	0.485
D9. There is a lack of staff participation and training in concrete recycling	2.76	0.94	3.16	1.00	1.80	0.074
Issues related to recycled concrete products
D10. Recycled products are of poor quality (e.g., reduced compressive strength)	2.23	1.13	3.34	1.09	4.12	0.000a
D11. There are limited applications in using recycled concrete products	2.61	1.19	3.51	1.07	3.33	0.001a
D12. There is an imbalance of supply and demand on recycled products	3.25	1.45	3.26	1.03	0.03	0.975
D13. There is insufficient research invested in concrete recycling products	3.13	1.12	3.43	0.92	1.14	0.255
Lack of support
D14. There is a lack of support in technologies, resources, training, competent staff regarding recycling concrete	3.17	1.24	3.10	1.10	0.24	0.807
D15. Our clients do not ask for the use of recycled concrete	3.14	1.28	3.42	1.09	0.95	0.344
D16. There are not enough concrete recycling companiesb	2.90	1.45	2.98	1.13	0.24	0.814
D17. There is a lack of industry awareness and support toward concrete recycling	3.05	1.17	N/A	N/A	N/A	N/A
D18. There is a lack of governmental awareness and support toward concrete recycling	3.82	1.22	3.27	0.99	2.01	0.046a
D19. There is a lack of certain regulatory standards regarding concrete recycling	2.95	1.32	3.48	0.96	1.73	0.086

aDenotes items with significant differences between Japanese and Australian surveys from Tam’s study (2009).

Significant differences were found in the survey results between this study and [8] concerning the following items:

•	Compared to the survey respondents in the U.S., the Australian and Japanese survey participants were more concerned about the higher cost of removing concrete waste (shown in D4). This was consistent with the early finding in Table 3 where B3) Reducing project costs by using recycled materials, was ranked low by Australian and Japanese survey participants (5th and 8th, respectively) in the benefits of recycling concrete. Comparatively, the cost of recycling concrete seemed to be more affordable in the U.S. than in the other two countries.

•	Both Australian and Japanese survey participants perceived more difficulties in recycling concrete. These difficulties lay in the quality issues and limited applications of recycled concrete products.

•	The U.S. survey participants were more concerned about the lack of government awareness and support toward concrete recycling than their counterparts in Australia and Japan.

Recommended methods in concrete recycling

In total, nine items were included in the section of recommended methods in concrete recycling. The survey questions, results, and statistical comparisons are displayed in Table 4. Participants in the U.S. survey gave high scores to R2) Identifying and classifying various uses of recycled wastes, R4) Considering concrete recycling in design, and R3) Developing techniques and the best management practices for recycling concrete. Actually, only two items in this section were not recommended by respondents. They were R5) Improving concrete recycling management in your organization, and R6) Providing in-housing training on concrete recycling. It seemed that companies cared more about the external measures/support in improving concrete recycling than their internal actions (i.e., organization management and training of employees). The U.S. survey participants deemed methods R4) Considering concrete recycling in design, R7) Effective communication on concrete recycling among all parties, and R9) High landfill charges for disposing concrete waste, more effective in improving concrete recycling than survey respondents in Japan and Australia.

Table 4. Survey results of recommended methods in concrete recycling

Recommended methods	U.S. This survey	Australia & Japan (Tam, 2009)	Statistical test results
Mean	Std	Mean	Std	z	p
R1. Comprehensive and accurate evaluation of concrete recyclingb	3.39	1.14	3.30	0.98	0.32	0.750
R2. Identifying and classifying various uses of recycled wastes	4.15	0.93	3.72	0.84	1.95	0.053
R3. Developing techniques and best management practices for recycling concrete*	3.90	0.91	N/A	N/A	N/A	N/A
R4. Considering concrete recycling in design	4.10	0.91	2.81	0.99	5.00	0.000a
R5. Improving concrete recycling management in your organization	2.84	1.01	3.17	1.02	1.33	0.185
R6. Providing in-house training on concrete recyclingb	2.65	0.99	2.93	0.95	1.19	0.237
R7. Effective communication on concrete recycling among all parties	3.68	0.89	3.23	0.96	2.04	0.043a
R8. Government restrictions on concrete waste volume generated onsiteb	3.17	1.38	3.40	0.99	0.68	0.495
R9. High landfill charges for disposing concrete waste	3.67	1.39	2.72	0.99	3.01	0.003a
R10. Government financial support for companies**	N/A	N/A	3.49	1.04	N/A	N/A

Note: *Item R3 was not included in Tam’s survey but recommended by the expert reviewers of the questionnaire.

**Item R10 was in Tam’s survey but was removed from this study based on the review feedback.

aDenotes p values lower than 0.05, which indicated significant differences between the compared countries.

bItems with significant differences between Japanese and Australian surveys from Tam’s study (2009).

Conclusion and recommendations

This study explored the status of concrete recycling in the U.S. by adopting a questionnaire survey approach. It also statistically compared the results between this survey and similar surveys [8] investigating concrete recycling in Australia and Japan. The survey revealed that in the U.S., waste concrete (mainly from the demolition of old buildings/structures) had been largely recycled into aggregates and widely applied in backfill and roadbase. However, the use of recycled concrete aggregate (RCA) in new concrete production was still limited.

The survey results implied that the U.S. survey respondents had high perceptions on the items regarding the awareness of concrete recycling and recommended methods. However, most participating companies had neither in-house training programs for their employees nor formed specific recycling departments/divisions in their organizations. In light of recommended methods for concrete recycling, companies seemed to be in favor of the external influence/support from the government, other parties, and techniques to improve concrete recycling rather than better organization management and in-housing training.

Based on the literature review and comparisons performed in this study among the U.S., Australia, and Japan, it could be inferred that the U.S. is ahead of Australia in concrete recycling, but lags behind Japan, especially in using RCA in new concrete production for structural applications. In general, these three countries face different challenges in concrete recycling. The future research will recruit more statistical methods to further study the survey results in order to provide a more quantitative analysis of concrete recycling practice among the three different countries. For example, Relative Importance Index can be used to study the relative ranking of questions within each section. Cronbach’s alpha can be adopted to measure the internal consistency of items within each section.

Acknowledgement

The authors would like to thank Mr. W. Mac Ware (Builders Exchange of Central Ohio) and Mr. Mark Pardi (Ohio Ready Mixed Concrete Association) for providing expert reviews of the questionnaire used in this study.

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