CEL 774 IIT DELHI Construction pRACTICES ( Lecture 1-3) Concrete: Production B. Bhattacharjee CIVIL ENGINEERING DEPARTMENT IIT DELHI DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 1 General Outline ™Concrete Production. D Production Process D Batching. D Mixing. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 2 What is CONCRETE? – Ordinarily concrete is made by mixing an inorganic material known as cement with water together with natural sand or stone dusts and natural stones which may be uncrushed or crushed. Cement Sand/ Fine Aggregate Stone / Coarse Agg. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 3 CEMENT – Most commonly used cement is called Portland Cement patented in 1824 in England, when mixed with water, hardens, hence hydraulic cement . ™ Basic raw materials used in the manufacture of cement are calcium carbonate found in lime Stone or chalk, and silica, alumina and iron oxide found in clay or shale. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 4 AGGREGATES Cement-sand Mortar Aggregate Aggregates forms the skeleton matrix 60-75% by volume. 25-40% Paste 1-2% Voids. ¾Aggregate shall be inert and strong. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 5 ADMIXTURES ™ Chemical Admixture: Used for specific Property/performance enhancement. ™ Mineral Admixture: Used for improvement of long term strength and durability performance. ¾ Using above admixtures together, high Strength and high performance concrete Materials can be designed. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 6 ADVANTAGES AND DISADVANTAGES OF CONCRETE ™ Lower life cycle cost ™ Mould-ability ™ Robustness. ™Can be designed for desired property ™ Low tensile strength. ™Lower ductility (brittle) ¾ Concrete is most popular construction material. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 7 CONCRETE & COMPOSITES ™Normal strength Concrete ™High strength/performance concrete ™Ultra high strength concrete ™Fiber Reinforced Concrete. ™ Densified with small particle (DSP) ™Macro Defect Free (MDF) Matrix ™ Reactive Powder Concrete (RPC) ™Polymer Concrete (PC) ™Polymer cement concrete B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 8 CONCRETE COMPOSITES A Reinforcement Matrix Binder B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 9 DESIGNATION OF NORMAL STRENGTH CONCRETE – Concrete is designated through 28 day Standard cube compressive strength. ™In Indian Standard Code of practice (IS 456) a concrete is designated by its characteristic cube compressive strength at 28 days, the cube being cast, cured and tested in a standard manner. ‰Concrete is designated as M25 has a 28 day Characteristic standard cube strength of 25 MPa. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 10 PERFORMANCE OF CONCRETE ™ Normal strength concrete: ≤ 60MPa ™ High strength concrete: 60 ≤ f C ≤ 120MPa. ™ Ultra High strength concrete: ≥ 120MPa. ™ Performance at fresh state: Self Compacting ™ Long term durability performance. ¾ Concrete is a versatile construction material. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 11 SUMMARY ™ Concrete Material. V Natural aggregates, cement or cementitious and water and also admixtures. V Concrete composites. V Concrete is designated by characteristics 28 day cube compressive strength. V Performance of concrete at fresh, hardening and hardened state. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 12 Production Process Batching Mixing Transport Curing Placing Compaction Concrete QUALITY CONTROL IS MOST IMPORTANT B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 13 Batching – Batching is the process of measurement of specified quantities of cement, aggregates, water and admixture, i.e., ingredients of concrete in correct proportion. – Batching Process ‰1) Volumetric batching . ¾Not desirable except for small non engineered jobs ‰ 2)Weigh Batching (Mass basis, IS456:2000) B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 14 Batching Process – Batching by mass (weights) as reproducibility of loose volume is inadequate and is not economical . – Control and storage of materials Aggregate bins for storing aggregate. Silos for storing cement and cementitious materials B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 15 Batching Plant – Components of a Batching Plant –A) Aggregate bins for various types of aggregates. – B) Feeding mechanisms such as scrappers, conveyors or hoists etc. to transfer aggregate to scales (balances). – C) Balance and measuring system. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 16 Batching Plant – Components of a Batching Plant –D) Cement silos and a conveyor screw or bucket conveyor . – E) The storage tank for water and water measuring system . – F) Dispenser for chemical (liquid) admixture. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 17 Batching Plant B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 18 BATCHING PLANT Scrapper Fly ash silo Cement Silos Aggregate bins DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 19 BATCHING PLANT Screw Conveyors Control Room Mixer B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 20 BATCHING – Plant Type can be cyclic or continuous. – Plant Type can be automatic or manual – Accuracy: Recommendation of IS 456 is ±2% for the quantity of cement measured and ±3% for the quantity of aggregate, water and admixture being measured. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 21 PLANT CAPACITY – Capacity depends on ™1) size of the job; ™2) required production rate; and ™3) required standard of batching performance. ¾Capacity of the material handling system, bin size, batcher size and; mixture size and number controls the capacity Q=min(Q1, Q2, Q3, Q4…..) B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 22 INSTRUMENTATION AND MEASUREMENTS – mechanical lever system, load cells etc for measurements of mass. – Controlling the discharge from storage and weigh hoppers is through gates operated by compressed air cylinders. – Presetting of desired batch weights can be done by devices such as punched cards, digit switches or rotating dials and computers. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 23 INSTRUMENTATION AND MEASUREMENTS – Electrical or microwave moisture gauges can be used as aggregate moisture meters . – Water is most commonly measured through flow meters, although in some plants water is also weighed . – With the need of adequate calibration, frequent regulatory routine and specialist’s checks of weighing process are required without too much difficulty . B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 24 TOLERANCES (individual Batch IS 4925) Ingredient Batching tolerances (%) Cement and other cementitious materials ±1 Water (by volume or weight),% ±1 Aggregates, % ±2 Admixture (by volume or weight),% ±3 B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 25 TOLERANCES (individual Batch) tolerances applies to: Minimum weight (kg) = [0.3×scale capacity (kg)] /Weigh tolerance (%) as in table ƒUniform concrete exhibits less variation. ƒVariation depends on variation in proportions •e.g., higher ΔC and ΔW, the errors in cement & water measurements will result in higher variation in strength. ‰Proper Batching ensures better quality B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 26 MIXING – Thorough mixing is essential for production of uniform quality concrete. – Equipment and method should be capable of effectively mixing concrete material containing largest specified aggregate to produce uniform mixtures of the lowest slump practical for the work. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 27 MIXING – cyclic or batch mixers, and continuous mixers. . – gravity mixers or mixers with forced movements o They can be tilting or Non-tilting – Counter-flow mixer or open–pan mixers B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 28 TILTING DRUM MIXER B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 29 NON-TILTING DRUM MIXER B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 30 PAN MIXER B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 31 PAN MIXER B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 32 MIXING – uniformity tests on samples of fresh concrete collected from the mixer at different stages of its discharge from a given batch. . – Charging: pre-blending and ribboning effect – Mixing Time: 1minute is required for 0.75 m3 capacity mixer and 0.25 minute is required for each additional 0.75 m3 capacity B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 33 MIXING TIME – IS guide lines ■IS 4925-1968 “mixing time for each batch of materials, except the full amount of water, provided that all the mixing water shall be introduced before one-fourth the mixing time elapsed” shall be 1½, 2 and 2½ minutes respectively for mixer capacity up to 2 m3, 3 m3 and 4 m3 respectively. IS 456 : 2000 guidelines specifies a overall minimum mixing time of 2 minutes B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 34 MIXING TIME –increasing mixing time may result in more uniform distribution of hydration product resulting in higher compressive strength –prolonging the mixing process too long may not increase the strength proportionally and may result in a decrease in some cases. –over grinding of the material and in some cases may increase the proportion of fines. Quite often excessive mixing leads to segregation in case of leaner concretes. B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 35 – Strength & Variance MIXING TIME Strength Variance – Time B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 36 SUMMARY – Concrete production process –Batching process and its importance in producing quality concrete –Mixing process for producing uniform quality concrete B. Bhattacharjee DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 37 THANK YOU FOR HEARING DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI 38