Construction Materials - Chapter 2 Aggregates (PDF)

An-Najah National University Construction Materials CHAPTER TWO AGGREGATES Aggregates: Are granular mineral particles used either in combination with various types of cementing material to form concretes or alone as road bases, backfill… etc. Aggregate sources: - Natural sand and gravel depo...

An-Najah National University Construction Materials CHAPTER TWO AGGREGATES Aggregates: Are granular mineral particles used either in combination with various types of cementing material to form concretes or alone as road bases, backfill… etc. Aggregate sources: - Natural sand and gravel deposits - Crushed rock - Slag and mine refuse - Rubbles and refuse - Artificial and processed materials - Pulverized concrete ‫الخرسانه المسحوقه‬and asphalt pavements - Other recycled and waste materials. Natural sand and gravel deposits: Consist of: - Sand or gravel soils that have been naturally sorted or sometimes need some processing. - A deposit might be composed of many different types of mineral particles such as limestone, sandstone, granite depending on the original bedrock source of the particles. Types of bedrock: 1) Igneous rocks: formed from the cooling of molten material, examples of these rocks granite, basalt and trap rock. Trap Rock Basalt 2) Sedimentary rocks: formed from the solidification of chemical or mineral sediments deposited under ancient seas, example of these rocks limestone, dolomite, shale, sandstone, gypsum, conglomerate and chert. Limestone Sandsto ne ‫الصوا‪Chert‬‬ ‫ن‬ 3) Metamorphic rocks : are igneous or sedimentary rocks that have been changed due to intense heat and pressure, example of these rocks slate ‫اردواز‬, marble, quartzite and gneiss ‫ النايس صخر صواني‬. Note: Igneous and Metamorphic rocks are usually very hard and make excellent aggregates for most purposes. ‫اردواز‪Slate‬‬ Quartzite Gneiss White Marble Slag: Is a waste material resulting from the treatment of Ore‫ خام‬to produce iron, steel, nickel, copper, gold … etc. Artificial and processed materials: Many types of rock or industrial materials are used for aggregates in special cases such as Expanded slag, shale‫ السجيل‬and plastic. Pulverized ‫مسحوق‬concrete and asphalt pavements: - The use of pulverized concrete from pavements, sidewalks and buildings being demolished is growing both due to increased cost of natural aggregates and desire to recycle rather than landfill these materials. - The proportion may be limited to about 30 -50 % in base courses as the strength can be reduced due to lubricating effect. Other recycled and waste materials: The use of other recycled materials such as crushed glass, rubber pellets, bricks, building rubble, and incinerator‫ محروقه‬waste is currently being investigated. ee Aggregate terms and types: - Fine aggregate: (sand size), aggregate particles mainly between 4.75 mm (no 4 sieve) and 75 µm (no 200 sieve). - Coarse aggregate: (gravel size) , aggregate particles mainly larger than 4.75 mm (No 4 sieve). - Pit run aggregate: sand or gravel pit, with no processing. - Crushed gravel - Crushed rock - Screenings: the chips, dust or powder that are produced in the crushing of bedrock for aggregates. - Concrete sand: sand washed to remove dust and fines - Fines: silt, clay or dust particles smaller than 75 µm (No 200 sieve). he Fineness modulus (FM) is an empirical figure obtained by adding the total percentage of the sample of an aggregate retained on each of a specified series of sieves, and dividing the sum by 100. The sieve sizes are 150 μm, 300 μm, 600 μm, 1.18 mm, 2.36 mm, 4.75 mm, 9.5 mm, 19.0 mm, 38.1 mm and larger increasing in the ratio of 2:1. The same value of fineness modulus may therefore be obtained from several different particle size distributions. In general, however, a smaller value indicates a finer aggregate. Fine aggregates range from a FM of 2.00 to 4.00, and coarse aggregates smaller than 38.1 mm range from 6.50 to 8.00. Combinations of fine and coarse aggregates have intermediate values. To find fineness modulus of coarse aggregate we need sieve sizes of 75mm, 37.5mm, 19mm, 9.5mm, 4.75mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm and 0.15mm. Example The test result on an aggregate to be evaluated as a highway base coarse are as followa: Gradation test: Passing 25 mm(1 in) 100% 19 mm (3/4 in) 98% 12.5mm (1/2 in) 81% 9.5 mm (3/8 in) 63% 4.75 mm (No.4) 48% 1.18 mm (No 16) 35% 300 micro m(No.200) 24% 75 micro m (No.200) 11% Example con. Abrasion test Original mass 5009 gm Final mass 3267 gm Soundness test Original mass 2649 gm Final mass 2115 gm Check for aggregate acceptability according to the specifications above? Solution Gradation test does not meet requirements for sieves: 300 micro m(No.200) 24% 75 micro m (No.200) 11% Abrasion test meets requirements %loss = {(5009-3267)/5009}x100 = 34.8%18% Blending  To meet the gradation requirements  By trial & error Example The percentages of each size of aggregates are shown bellow: Size (mm) Sample 1 Sample 2 specification 12.5 100% 100% 100% 9.5 60% 70% 65-80% 4.75 10% 60% 40-50% Show the percentages of each sample to obtain the required specifications? Solution Blend 30% of sample 1 with 70% of sample 2. then the result will be tabulated in the following table: Size (mm) Sample 1 Sample 2 blending sample specification 12.5 30%x100%=30% 70%x 100%=70% 100% 100% 9.5 30%x 60%=18% 70%x 70%=49% 67% 65-80% 4.75 30%x10%=3% 70%x 60%=42% 45% 40-50% As shown, the blending sample meets the required specifications. Sieve size (nominal size): - A term often used in describing and specifying aggregate. - Size determination by sieves for aggregate is based on the mass retained and passing each sieve. - A small amount , usually 5% or 10% is allowed to be either larger or smaller than the specified size. - A single-size coarse aggregate is called CLEAR. Aggregate Strength: - Aggregates are used mainly: a) as layers of particles to distribute imposed loads over the surface of the soil. b) or as economical filler material in concretes. - The strength of aggregate particles themselves is not a factor, the shape of the particles is more important. - Crushed particles better than rounded particles because of a the high friction between the crushed particles and less sliding over each other, and better in distributing loads. - Densely graded aggregate layers increase the strength developed because of the high frictional resistance to shearing failures.