الدكتور محمد طه السيد أحمد • حاصل على البكالوريوس في الهندسة المدنية من جامعة القاهرة 1979 • حاصل على الماجستير في هندسة الانشاءات من جامعة نورث كارولينا 1984 • حاصل على الدكتوراه في الهندسة الجيوتقنية من جامعة اوهايو 1992 • مدرس ورئيس قسم وعميد في البوليتكنك منذ عام 80 وحتى 96 • مؤسس ومدير المركز الدولي للدراسات الهندسية والجيولوجية (الخليـل و بيت لحم وأريحا) • حاصل على شهادة المجمع البريطاني للتحكيم • خبير مسجل في وزارة العدل الفلسطينية • خبير تحكيم مسجـل في اتحاد المنظمات الهندسية في الدول الإسلامية • خبير تحكيم مسجـل في المركز العربي للتحكيم بالقاهرة • عضو مؤسس ورئيس جمعية الخرسانة الفلسطينية • عضو هيئة مكتب نقابة المهندسين 1997-2003 • عضو معهد الخرسانة الأمريكي ACI • عضو جمعية المواد والفحوصات الأمريكية ASTM • عضو شرف في جمعية المهندسين المدنيين الأمريكية ASCE • عضو جمعية موظفي الطرق الأمريكية AASHTO • عضو جمعية أعمال هندسة المياه الأمريكية AWWA • عضو في العديد من لجان المواصفات الفلسطينية • عضو في العديد من لجان اتحاد المهندسين العرب والفدرالية العالمية للمهندسين
Uses and Benefits of Recycled Concrete Aggregate (RCA) By Mohammad T. Alsayyed Presented at An Najah University Nablus April 18th, 2011
Studies have revealed that concrete is the most commonly used product after drinkable water.
Recycled Concrete What is it ? Demolition by-product of old concrete structures such as: Roadways Sidewalks Foundations Retaining Walls Concrete Pipes Roadway Medians Bricks etc properly processed so that it can be used as a substitute aggregate material OR Hardened concrete that has been processed for reuse, usually as aggregate
What is the world doing to recover concrete? • The Netherlands is an example of where landfill of concrete waste is banned. All concrete is recycled except for some residual process waste. • 38 states in the US use recycled concrete aggregate for road sub-base and 11 recycle it into new concrete. • Brazil has some recycling facilities. Recycled aggregate is used mainly for road sub-base. Legislation exists promoting C&DW management.
In Finland strong legislation and enforcement means that all recyclable material from a demolition site must be recycled. • Kosovo had 10 million tons of building debris following the end of hostilities. A project was established to produce and promote recycled aggregate for the rebuilding effort. • Japan has near complete recovery of concrete from C&DW. Almost all is used for road sub-base.
Qatar and UAE have developing recycling programs to produce aggregate. The cost of virgin aggregates drives the process in Qatar. In the UAE, environmental concerns and government restrictions on waste are the main drivers. • China is seeing increasing interest in concrete recovery and it is estimated that about 90% of C&DW is recovered, with a rate of 95% for concrete.
Factors to consider when comparing recycled aggregate to virgin aggregate or other building materials include: • Transportation costs including fuel usage • Noise, air pollution and the energy needs of the processing systems to recover the concrete or use natural materials • Land Use Impact – Using recycled aggregate means • Less waste goes to landfill • Less land is disturbed as virgin alternatives can be conserved. • Environmental impacts during the use phase Recycled aggregate has similar properties to regular virgin concrete. As such there is usually less difference in impact from this perspective during the use phase. • Useful life expectations The durability of concrete and recycled concrete means that its long useful life can be a sustainability benefit compared with other materials.
Physical Properties Gradation (Same as conventional) Specific Gravity (increases with size 2.0-2.5) Shape (more angular, good) Texture (rougher, good) Moisture Content (higher due to absorption) Compacted Density (optimum w% higher) Absorption (decreases with size, 8 to 2%)
Mechanical Properties Strength (CBR 90 to 140) Equal Abrasion Loss (LAB 20 to 45) Increases
Benefits of recycled concrete Conserves natural resources, reduce the amount of waste sent to landfills Good for the environment, around 135 million tons/year of construction demolition waste material in USA Can be good business as it is expected to grow.
Recycled Aggregate Products & Applications Products: Road Base Structural Backfill Landscape Stone Vehicle Tracking Rock Ready Mixed Concrete Top soil improvements Under Slab Bedding Stackable Landscape Stone Pipe Bedding
Applications: • A- without any processing: • many types of general bulk fills. • bank protection. • 3. base and fill for roads construction. • 4. noise barriers. • B- after processing and removal of allcontaminants: • 1. new concrete for shoulders, median barriers, sidewalls, curbstones, … • 2. Structural concrete. • 3. pipe bedding. • 4. landscape works – in large broken pieces or after crushing. • 5. roads. • 6. wall backfill. • 7. retaining walls (gabion types)
RCA Stockpiles Ready for use
Problems Contaminants: removal of steel or other non-concrete materials such as asphalt, soil and clay balls, chlorides, glass, gypsum boards, sealants, paper, plaster, wood and roofing materials is relatively expensive and time consuming. Cost: according to environmental council of concrete organizations, concrete costs up to 4$/ton to crush (USA). Strength: 8090% of strength compared with concrete from raw materials. (In recent studies, this was improved). Water absorption 2-6% more than new concrete.
Obstacles and Barriers to Using RCA Need a specifications for use Must recognize differences Q/C – Q/A Commitment to use must be made High initial investment Concrete crushers Additional equipment for metal removal Maintenance costs of concrete crushers Excess amount of fine RCA Fine RCA includes a significant amount of mortar particles, not durable aggregate
ConcreteMix Design Using RCA The quality of concrete with RCA is very much dependent on the quality of the recycled material. It is generally accepted that up to 30 % of natural crushed coarse aggregates can be replaced when using the natural sand, without affecting the mechanical properties. water reducer has to be increased to achieve slump, workability as in conventional. saturate the aggregate to saturated surface dry when use in the mix. 10-20% of the fine aggregate produced from RCA can be used, several mixes should be tried.
Durability Indicators Carbonation Resistance to Chloride Penetration Permeability Resistance to Corrosion Alkali Aggregate Reaction
Crushers Some mobile crushers can crush up to 600 tons/hr. Mini-Crushers can crush up to 150 tons/hr.