MIX DESIGN OF HIGH STRENGTH CONCRETE, SPECIAL CASES IN MIX DESIGN. Exercise 7. Introduction

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1 MIX DESIGN OF HIGH STRENGTH CONCRETE, SPECIAL CASES IN MIX DESIGN Exercise 7 Introduction The strength of high strength concretes is K70 K100 (By50). Ultra high strength concrete (RPC aka Reactive Powder Concrete) contains: rock powder as aggregate with steel dust and steel fibres which compact the concrete so that it can reach strengths of up to 800 MPa. Low water/cement ratio: below 0,35 even below 0,20

2 Introduction High strength concretes are composed of same materials as normal strength concretes. the selection of cement and additives is based on: The desired strength gain and heat development The used aggregate contains only small amounts of fines and silt. Due to the high amount of binder and that the aggregate grading does not have as big influence as in normal strength concrete. Requires the use of water reducing admixtures (superplasticizers) Requires careful curing Mix design of High Strength Concrete 1. Define proportioning strength of concrete 2. Define the amount of binder and Calculate the amount of cement and additional binders 3. Define the amount of (super)plasticizer 4. Define the amount of water 5. Calculate the amount of aggregate with the volumetric equation of concrete 6. Combine the aggregate 7. Define the components of the batch and make a trial batch

3 1. Define proportioning strength of concrete f m = f c + ks f m = the target mean strength f c = the specified characteristic strength s = the standard deviation, and k = a constant The constant k is derived from the mathematics of the normal distribution and increases as the proportion of defectives is decreased, thus: k for 10% defectives = 1.28 k for 5% defectives = 1.64 k for 2.5% defectives = 1.96 k for 1% defectives = 2.33 BRE - Building Research Establishment, UK Design of normal concrete mixes 1. Define proportioning strength of concrete It is generally accepted that at a given level of control the standard deviation increases as the specified characteristic strength increases up to a particular level the standard deviation being independent of the specified characteristic strength above 20 N/mm2. BRE - Building Research Establishment, UK Design of normal concrete mixes

4 2. Define the amount of binder and calculate the amount of cement and additional binders C = cement Si = Silica fume Lt = Fly ash Mk = Blastfurnace slag Binder amount (C+2,5 Si+0,3 Lt+Mk) - use the mineral admixtures proportion of the cement to calculate the amount of cement, silica, fly ash and blast furnace slag From the report: Korkealujuuksisten betonien suhteitus ; Penttala V. et. al. (1990). 3. Define the amount of (super)plasticizer The amount of plastizer as proportion of the binder is defined based on the target mean strength (proportioning strength) From the report: Korkealujuuksisten betonien suhteitus ; Penttala V. et. al. (1990).

5 4. Define the amount of water Curves determine the (wateradmixture air / binder) ratio of high strength concrete The proportioning strength is K 28 The compressive strength is determined using 100 mm cubes The amount of air is assumed to be 10 dm 3 /m 3 Amount of admixture from STEP 3 From the report: Korkealujuuksisten betonien suhteitus ; Penttala V. et. al. (1990). 5. Calculate the amount of aggregate Calculate the amount of aggregate with the volumetric equation of concrete. The amount of air is assumed to be 10 dm 3 /m 3 C = cement Si = Silica fume Lt = Fly ash Mk = Blastfurnace slag I = air content Nt = Plasticizer W = Water R = Aggregates

6 6. Combine the aggregate 7. Define the components of the batch and make a trial batch

7 the mix design process The guidelines of the mix design are drawn up for 100*100*100 mm cubes Binders: Cement k cem 1 Blast furnace slag k MK 1 Fly ash k LT 0,3 Silica k sil 2,5 The mix design guidelines are for concretes of consistency 2-3 svb ( S3/S2)

8 Exersice 1 Proportion a K100 concrete (at the age of 28 days) with CEM I as binder with 8 % silica fume. INPUT: K28 = 100 MPa Cement type = CEM I Silica amount = 0,08 * cement [kg/m³] 1) Proportioning strength f m = f c + ks f c = 100 MPa k for 10% defectives = 1.28 s for 100MPa and less than 30 samples = 8 MPa fm = *8 = f m = 110MPa

9 2) Define the amount of binder Amount of binder is 630 kg/m 3 2. Calculate the amounts of cement and additional binders from the binder amount (in this case the amounts of cement and silica). Binder amount (C+2,5 Si+0,3 Lt+Mk) Si = 8% cement, Lt and MK = 0% C+2,5 0,08C = 630 C(1+0,2) = 630 C = 525 kg/m 3 and Si = 42 kg/m 3

10 3) Define the amount of (super) plasticizer Amount of plasticizer is 3,3 % (C+Si) 0,033*(525+42) = 18,7 kg/m 3 Lt and MK = 0% 4) Define the water amount We get (W+Nt+I)/S = 0,25 (W+Nt+I)/(C+2,5*Si) = 0,25 (W+18,7+10)/(525+2,5*42) W = 0,25(630) 18,7 10 W = 128,8 kg/m 3 Binder amount (C+2,5 Si+0,3 Lt+Mk)

11 5) Calculate the amount of aggregate +W+ N +Air =1000 Thus,, + 128,8 + 18, , +, = 1000 Q AGG = ( ,8 18, ,4 19,1) * 2,68 Q AGG = 654 dm 3 = 1753 kg/m 3 Ex 1 - Mix design ingredient kg/m³ Cement 525 Silica fume 42 Fly ash -- W/C = 0,25 W/B = 0,23 GGBS -- Water 128,8 Superplasticizer 18,7 Aggregates 1753

12 Exersice 2 Proportion concrete for which the reference strength for 150 mm cubes is 55 MPa at the age of 1 day. As binder use CEMI, 10 % silica fume and 30 % fly ash. INPUT: K28 =???? Cement type = CEM I Silica amount = 0,10 * cement [kg/m³] Fly ash amount = 0,30 * cement [kg/m³] 1) Proportioning strength The guidelines of the mix design are drawn up for 100*100*100 mm cubes. For 100 mm cubes the compressive strengths are about 5 % greater than for 150 cubes For 100 mm cubes the compressive strengths should thus be f m = 55*1,05 = 58 MPa The standard deviations of the strength of the 100 mm cubes are higher than that of the 150 mm cubes. The mean standard deviation of the strength of the 150 mm cubes are about 4 MPa f m = *4 = 63 MPa à 1d strength

13 1) Proportioning strength The compressive strength at 28 days f s at the age of 28 days is 85 MPa 2) The amount of binder from figure Amount of binder is 440 kg/m 3

14 2) The amount of binder INPUT: Silica amount = 0,10 * cement [kg/m³] Fly ash amount = 0,30 * cement [kg/m³] The amount of binder (C + 2,5Si + 0,3Lt) = 440 Si = 0,1C Lt = 0,3C C (1 + 2,5*0,1 + 0,3*0,3) = 440 C = 328,4 kg/m 3 Si = 32,8 kg/m 3 Lt = 98,5 kg/m 3 3) define the amount of plasticizer Amount of plasticizer 2,8 % 0,028*(328,4 + 32,8 + 98,5) = 12,9 kg/m 3

15 4) Define the water amount We get: (W+Nt+I)/S = 0,39 (W+12,9+10)/(440) = 0,39 W = 0,39(440) 12,9 10 W = 148,7 kg/m 3 5) Calculate the amount of aggregate +W+ N +I = 1000 Thus,, + 148,7 + 12, ,, +,, +,, = 1000 Q AGG = ( ,7 12, ,9 14,9 42,8) * 2,68 Q AGG = 664,8 *2,68 = 1782 kg/m 3

16 Ex 2 - Mix design ingredient kg/m³ Cement Silica fume 32.8 Fly ash 98.5 W/C = 0,45 W/B = 0,34 GGBS -- Water Superplasticizer 12.9 Aggregates 1782 Exersice 3 How would you change the mix design if the measured consistency of the concrete was 4 svb and the 1st day strength was 58 MPa? INPUT: K28 =???? Consistency = 4 svb Cement type = CEM I Silica amount = 0,10 * cement [kg/m³] Fly ash amount = 0,30 * cement [kg/m³]

17 1) Proportioning strength For 100 mm cubes the compressive strengths are about 5 % greater than for 150 cubes f m = 58*1,05 = 61 MPa The mean standard deviation of the strength of the 150 mm cubes are about 4 MPa f m = *4 = 66 MPa à 1d strength 1) Proportioning strength From the chart, we can notice that: 1 day f s = 66 Mpa f s at the age of 28 days is 90 MPa

18 2) The amount of binder New amount of binder is 460 kg/m 3 2) The amount of binder INPUT: Silica amount = 0,10 * cement [kg/m³] Fly ash amount = 0,30 * cement [kg/m³] The amount of binder (C + 2,5Si + 0,3Lt) = 460 Si = 0,1C Lt = 0,3C C (1 + 2,5*0,1 + 0,3*0,3) = 460 C = 343,3 kg/m 3 Si = 34,3 kg/m 3 Lt = 103 kg/m 3

19 3) amount of plasticizer BY 15 (old) BY 50 (new) 3) amount of plasticizer New plasticizer amount is 3,0 % but because the previous concrete mix was too stiff, we ll raise the amount of plasticizer to 3,2 % 0,032*(480,6) = 15,4 kg/m 3

20 4) water amount : (W+Nt+I)/S = 0,35 (W+15,4+10)/(460) = 0,35 W = 0,35(460) 15,4 10 W = 135,6 kg/m 3 4) Calculate the amount of aggregate +W+ N +I = 1000 Thus,, + 135,6 + 15, ,, +,, +, = 1000 Q AGG = ( ,6 15, ,7 15,6 44,8) * 2,68 Q AGG = 667,9 *2,68 = 1790 kg/m 3 C = 343,3 kg/m3 Si = 34,3 kg/m3 Lt = 103 kg/m3

21 Ex 3 - Mix design ingredient kg/m³ Cement Silica fume 34.3 Fly ash 103 W/C = 0,39 W/B = 0,29 GGBS -- Water Superplasticizer 15.4 Aggregates 1790 Exersice 4 Which matters should be taken into consideration when proportioning pumpable concrete? How about concrete with high wear resistance (kulutuskestävyys)?

22 Pumpable concrete The grading of the aggregate should be continuous Bleeding is usually a result of non-continuous grading or coarse sand which causes discontinuity between the finest material. Sufficient amount of fine material (cement, additional binders, filler), using of crushed aggregate increases the needed amount of fines. Cement kg/m 3 Amount of fines <0,25 mm: kg/m 3 Consistency S4 S2 (S1) Use of plasticizers improves pumpability Air entraining agents may hinder it The amount of air is decreased during pumping The maximum size of aggregate 1/3 of the size of the distributing pipe

23 High abrasion (wear) resistance Abrasion damage occurs when the surface of concrete is unable to resist wear caused by rubbing and friction. As the outer paste of concrete wears, the fine and coarse aggregate are exposed and abrasion and impact will cause additional degradation that is related to aggregate-to-paste bond strength and hardness of the aggregate. Although wind-borne particles can cause abrasion of concrete, the two most damaging forms of abrasion occur on vehicular traffic surfaces and in hydraulic structures, such as dams, spillways, and tunnels. High abrasion (wear) resistance The hardened cement paste is the weakest link, the aggregate the most durable The aim is to use as much aggregate as possible Lower the amount of material passing the sieves 0,125mm and 4mm Avoid too plastic concrete compositions Use of plasticizers Sufficient strength