Use of High Performance Super Plasticizer in Concrete

Transcription

1 Use of High Performance Super Plasticizer in Concrete Theme No. & Description : 6, Innovative Materials & Technology Reference No. : 74 Name of Author : Mr. Mayank Rawal/Dr. S.C. Maiti Abstract : Chemical admixtures have become essential component of concrete especially of high performance concrete that exhibit durability high mechanical strength & workability. Super plasticizers are the most important class of chemical admixtures, which improve the physical properties of fresh concrete. The extensive comparison of the performance of poly carboxylic based admixture developed indigenously has been made with the commonly available Poly Naphthalene Sulfonate & Poly Melamine Sulfonate products. The paper also discusses the importance of the chemical functional group present & molecular weight distribution of the chemical admixture to achieve best results. The flowability of cement paste using Mini slump cone at constant water-cement ratio has been reported Contd..2

2 - 2 - Name of Author : Mr. Mayank Rawal Qualification : B.E. (Chemical Engg.) Designation : Director (Technical) Address : Asian Laboratories, 88, New Okhla Industrial Complex, DSIDC Shed, Scheme I, Phase II, New Delhi Telephone : Mob. No. : asianlab@vsnl.net Name of Author : Dr. S.C. Maiti Qualification : P.H.D. Civil Engineer Designation : Ex-Joint Director Address : National Council for Cement & Building Material, Ballabhgarh Mob. No. : Contd.3.

3 - 3 - INTRODUCTION : The invention of super plasticizers is one of the most important breakthrough that has led to the development of high performance concrete. Super plasticizers can be used in concrete for their different purposes as described below :- to increase workability, at a given mix composition in order to entrance placing characterstics of concrete. To reduce the mixing water, at given cement content and workability in order to reduce the water cement ratio (w/c) and therefore to increase strength and improve durability. To reduce both water and cement, at given workability and strength, in order to save cement and reduce creep, shrinkage and thermal strains caused by heat of cement hydration. Recently advances in super plasticizers containing functional group based on the family of Poly Carboxylate Polymer (PC) have been studied to reduce the slump loss drawback. Besides a lower slump loss, PC based super plasticizers perform better than the traditional Sulfonated Polymers in terms of higher water reduction and lower slump loss. The mechanism of action of super plasticizers has proved that the negatively charged anionic polymer such as Sulfonated Naphthelene Formaldehyde (SNF) for the presence of SO3 groups on the surface of cement particles imparts strong dispersion effect. The dispersion mechanism performed by PC based super plasticizers could be related more to a steric hinderance effect (Produced by the presence of neutral side long graft chains) rather than to the presence of negatively charged anionic group (COO ) which are responsible for the adsorption of the polymers on the surface of cement particles Schematic picture of Sulfonated Polymer and Poly Carboxylate Super Plasticizer & their effects on cement are shown in fig. 1 and fig. 2 respectively. Materials Although many brands & types of cement are tested for the sake of brevity only the result of the typical cements are discussed i.e. an Ordinary Portland Cement as per I.S.:12269 (53 grade) and Slag cement as per I.S.:455. Table-1 shows the properties of these two types of cement. In the design of concrete mix, sand of zone-ii having fineness modulus of 2.6 and gravel aggregate of max. size of 20 mm were used, with approx. 40% of sand and 60% gravel aggregate by mass respectively. Contd.4

4 - 4 - In the design of concrete mix, sand of zone-ii having fineness modulus of 2.6 and gravel aggregate of max. size of 20 mm were used, with approx. 40% of sand and 60% gravel aggregate by mass respectively. Super Plasticizer The Poly Carboxylated Polymer was synthesized using acrylic acid co-polymer to achieve average mol. Wt. of 5x10 4. The properties of the concentrated solution of the PC, Poly Carboxylate Polymer and the commercial available SNF super Plasticizers are given in Table-2.. Rheological Properties. The evaluation of the dispersion effect in cement paste was carried out by using empirical mini slump test. Cement pastes were prepared by mixing water and the Super plasticizers at various dosages from 0.5, 1.0 and 1.5% using fixed water/cement ratio of 0.25 with slag cement. In order to evaluate the mini slump retention duration time, each cement paste was kept for 30 min., 60 min., 90 min. and 120 minutes respectively. The standard mixing time for the mini slump test was kept as one minute before it was poured in a truncated cone mould standing on a flat surface. The cone was then lifted and the area (cm²) of the collapsed paste was measured. Concrete Mixing and Testing : Mixing of concrete was done by a laboratory mixer. All the ingredients were weighed and batched according to the mix proportion. 75% of water was added first and a time gap of around one minutes was given before adding the remaining 25% of water along with the super plasticizer in the mixing process. Each batch of concrete was tested for workability in terms of slump, immediately after mixing and at internal of 30, 60, 90 & 120 minutes. Concrete Cube specimens were tested for compressive strength at 3 day, 7 days & 28 days. Progress in Slump Retention :- The adsorption of super plasticizer can be related to viscosity. It is found that the slump value increased as the amount of adsorption increased. The adsorption is also greater at higher w/c ratio. The amount of adsorption also related to the mol. wt. of the super plasticizer and the Contd..5

5 - 5 - different chemical structures of the super plasticizers. Poly Carboxylate ether based super plasticizers gives maximum adsorption at 5.6x10 4 mol. Wt. compared to 1.6x10 4 mol.wt. for naphthelene formaldehyde condensate. The dosage of superplasticizer increases for equal workability once the mol.wt. is less or more than the optimum dosage as specified above. The fluidifying effect for cement paste could be increased by reducing the content of monomer. The amount of adsorption and the optional degrees of polymerization were different for admixture with different chemical structures. Concrete Cube specimens were tested for compressive strength at 3 day, 7 days & 28 days. Progress in Slump Retention :- The adsorption of super plasticizer can be related to viscosity. It is found that the slump value increased as the amount of adsorption increased. The adsorption is also greater at higher w/c ratio. The amount of adsorption also related to the mol. wt. of the super plasticizer and the different chemical structures of the super plasticizers. Poly Carboxylate ether based super plasticizers gives maximum adsorption at 5.6x10 4 mol. Wt. compared to 1.6x10 4 mol.wt. for naphthelene formaldehyde condensate. The dosage of superplasticizer increases for equal workability once the mol.wt. is less or more than the optimum dosage as specified above. The fluidifying effect for cement paste could be increased by reducing the content of monomer. The amount of adsorption and the optional degrees of polymerization were different for admixture with different chemical structures. Test Results & Conclusions : The P.C. based admixtures facilitate the production of concrete with low water/cement ratio with extended workability and using high volume fly ash. The solid content present in PCE admixture is only 25 to 30% compared to SNF based admixtures which is 42 to 45%. The consumption of PCE based admixture compared to SNF based admixtures on solid basis is just half (Table3) The flow properties of PCE admixtures at low dosage is higher at low water/cement ratio compared to SNF admixture (Figs 3 & 4). It is observed that PCE based admixtures compares to SNF based admixtures produces more plastic concrete free from big holes and air voids. Napthelene based Superplasticizer may slightly discolour white or other lightly coloured concretes. Contd.6

6 - 6 - REFERENCES 1. Tanaka, Y and Okazawa, S, A New Polycarboxylate Based Polymer- Chemistry and dispersing performance Concrete N. Spirates and C.J. Olicocur, Trends in concrete Chemical Admixture for the 21 st Centuary. SP Kantro, D.L. Influence of Water reducing admixture of Cement Paste A minimature slump test Cement and Concrete, aggregate Vol Rawal Mayank. High Performance Admixture as Super Plasticizer in Concrete Proceeding of ICFRC International Conference on Fibre Composites, High Performance Concretes and Smart Materials, 8-10 January 2004 Chennai, India pp Contd.7

7 - 7 - Table : 1 : Properties of 53 Grade Cement and Slag Cement Properties FINENESS Specific Surface (M²/Kg) SETTING TIME (Min.) a. Initial b. Final 53 Grade Cement OPC (As per Standard Specification : I.S.:12269) Slag Cement (As per Standard Specification:IS.:455) COMPRESSIVE STRENGTH (Mpa) a h b h c h STANDARD CONSISTENCY (%) Insoluble Residue (%) Magnesia (%) Sulphuric Anhydride (%) Loss on Ignition (%) Total Alkalities (As Na 2 O)(%) C3A (%) Contd..8

8 - 8 - Table-2 : Properties of the concentrated solution of SNF & PCE based super plasticizers. Type SNF PCE Colour Dark Brown Colourless to light yellow Solid Content % Specific Gravity ph Viscosity (Cps) Av. Mol. Wt. 6x10³ 5.5x10 4 Cement Dispersion -ve electrostatic Steric hinderence Contd..9

9 - 9 - Table-3 : Concrete properties using SNF & PCE Super plasticizers in a Ready Mix Concrete Plant Grade of M-50 M-50 M-50 M-25 M-25 Concrete Lab No Cement 400Kg Vik.53 OPC 400kg (Vik.53) OPC 500kg PPC Kaymore 270Kg OPC Kaymore 270Kg OPC Kaymore Silicafume 14 Kg 14 Kg Fly Ash 46 Kg 46 Kg 100 Kg 140 Kg 140 Kg Sand 710Kg 710 Kg Kg 750Kg 750Kg 10mm 424Kg 424 Kg 366.8Kg 414Kg 414Kg aggregate 20mm 636Kg 636 Kg Kg 621Kg 6212Kg aggregate Water 152 Kg 152 Kg 165 Kg 185 Kg 185 Kg W/C Admixture SP-3000 PCE SP-3000 SP-3000 PCE SP-3000 PCE 1% by volume PCE 0.65% 1.5% by 0.8% by SNF 1.2% by cement of cement by volume volume volume of Control Slump 0mm of cement 0mm of cement 0mm cement Control Slump -- Initial Slump 210mm 110mm Collapse Initial Slump After 30 min. 210mm 70mm -- After 30 min. Collapse -- After 2Hrs Collapse After 2Hrs 100mm After 3 Hrs Collapse After 3 Hrs. -- Compressive Strength of Concrete 3 days(n/mm²) 7days 28days Compressive Strength of Concrete 3 days(n/mm²) 7days 28days Contd.10

10 SNF Sulphonic group for electrostatic repulsion Side sulphonic group Main polymer chain SNF Cement grain Fig.1 Schematic picture of sulphonated Polymer (SNF) & its effect on cement grain Contd.11.

11 Main polymer chain Graft chain Steric hinderance Side long graft chain Responsible for steric hindrance Cement grains Fig.2 Schematic picture of Polycarboxylate superplasticizer (PCE) & its effect on cement grain Contd.12.

12 SNF Sulphonic group for electrostatic repulsion Spread Area Cm2 Side sulphonic group Main polymer chain % 0.4% 0.8% 1.0% Superplasticizer, % by wt. of Cement SNF SNF PCE Cement grain Fig.1 Schematic picture of sulphonated Polymer (SNF) & its effect on cement grain FIG.3 : Spread Area of Mini Slump cone at w/c = 0.25 Contd 13

13 Spread Dia.(cm) the spread Dia. of mortar SNF PCE SNF PCE SP/C (%) Fig. 4 : The Spread diameter of cement mortar with PCE and SNF Superplasticiser at w/c = 0.42

14 Use of High Performance Super Plasticizer in Concrete-II Abstract : Mr. Mayank Rawal Superplasticizer have become common component of concrete as the engineers have practically observed that the concrete properties can be significantly changed advantageously by incorporating super plasticizer. The extensive comparision of the performance of Poly Carboxylic based admixture developed indigenously has been made with the commonly available Poly Naphthelene Sulfonate & Poly Melamine Sulfonate Products. The papers discusses the further development in the production of Indigenious PCE based admixture* by studying the parameters of optimum molecular weight, functional groups to achieve best result. The flowability of cement paste using mini slump cone at constant water-cement ratio has been reported.. * 1 st part of the paper presented during ICI-Innovative World of concrete 2008 Mr. Mayank Rawal, Qualification : B.E. (Chemical Engg.) Designation : Director (Technical) Address: Asian Laboratories, 88, New Okhla Industrial Complex, DSIDC Shed, Scheme-I, Phase-II, New Delhi Ph Mob.: asianlab@vsnl.net, Asinlab88@gmail.com asianlaboratories@rediffmail.com

15 Kind Attn.: Mr. Elson Sub.: Submition of abstract Use of High Performance Superplasticizer in concrete-ii Dear Sir, Kindly recall the telephonic talk undersigned has with you, on the above subject during the 4 th International Conference on ICI-Innovative World of Concrete 08 held in Dec., 2008, India Expo Centre, Greater Noida. We had submitted paper on the above subject. We have carried out further studies on the indegeniously developed Poly Carboxylic based superplasticizer and presented our findings. Kindly acknowledge the receipt. Thanking you, Yours faithfully, For ASIAN LABORATORIES. MAYANK RAWAL DIRECTOR (TECH) Mob.: