role of minimum cement contents in concrete specifications ... · 09.04.2019 · total of 20...
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![Page 1: Role of Minimum Cement Contents in Concrete Specifications ... · 09.04.2019 · Total of 20 non-air concrete mixtures. 40% slag cement, 100% OPC, 25% Class F. Aggregate Voids Testing](https://reader031.vdocuments.us/reader031/viewer/2022011923/6060f79b36fa65272f303d06/html5/thumbnails/1.jpg)
Role of Minimum Cement Contents in Concrete Specifications and Mixture Proportioning
Karthik Obla
Spring 2019 National Concrete Consortium
Denver, CO
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Introduction
Should Minimum CM content be specified?
Mixture proportioning with low CM content
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Research Objective
Examine influence of CM content on concrete performance at specific w/cm
Parallel tests at Iowa State University
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Experimental Variables
w/cm: 0.40, 0.47, 0.55
CM – 417 to 720 lb/yd3
Paste: 22%, 24%, 27%, 31% at same CA/FA
Total of 20 non-air concrete mixtures
40% slag cement, 100% OPC, 25% Class F
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Aggregate Voids Testing (ASTM C29)
20%22%24%26%28%30%32%34%36%38%40%
0% 20% 40% 60% 80% 100%
Void
cont
ent,
%
% Coarse Aggregate Volume
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Concrete Tests ConductedSlump – add Type F HRWR if slump<1 in.
Air content, density, temperature, setting time
Compressive strength
RCPT (ASTM C1202)
RMT (AASHTO TP64)
Sorptivity (C1585)
Shrinkage (C157)
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Compressive Strength – 28 days
4000
5000
6000
7000
8000
9000
10000
400 500 600 700 800
Com
pres
sive
Stre
ngth
, psi
Total Cementitious Content, lb/yd3
0.55SL0.47SL0.40SL0.47FA0.47PC
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Compressive Strength – 1 day
0500
1000150020002500300035004000
400 500 600 700 800
Com
pres
sive
Stre
ngth
, psi
Total Cementitious Content, lb/yd3
0.55SL0.47SL0.40SL0.47FA0.47PC
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RCPT – 28 day AC
0
1000
2000
3000
4000
5000
400 500 600 700 800
RCPT
, cou
lom
bs
Total Cementitious Content, lb/yd3
0.55SL 0.47SL0.40SL 0.47FA
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RMT – 28 day AC
0.00
0.01
0.02
0.03
0.04
0.05
400 500 600 700 800
RMT,
mm
/V-h
r
Total Cementitious Content, lb/yd3
0.55SL0.47SL0.40SL0.47FA0.47PC
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Initial Sorptivity
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
400 500 600 700 800
Initi
al S
orpt
ivity
, x10
-4m
m/s
1/2
Total Cementitious Content, lb/yd3
0.55SL0.47SL0.40SL0.47FA0.47PC
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Drying Shrinkage – 90 days
0.025
0.035
0.045
0.055
22% 24% 26% 28% 30% 32% 34%
Leng
th C
hang
e, %
Paste Volume
0.55SL 0.47SL0.40SL 0.47FA0.47PC
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SummaryHigher CM contents increase mixing water demand
For given w/cm increasing CM content:
Same strength
Increased chloride penetrability, sorptivity, shrinkage
Does not appear to be a technical basis for specifying minimum CM content or a maximum w/cm when not needed
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Mixtures with Low CM contentHow low can you go?
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Mixtures with Low CM content
How low can you go?
Impact of air entrainment?
Impact of SCMs and WRA
Cast 12 more mixtures
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For water slump of 1 in. before WR addition
Minimum CM content for acceptable performance – Effect of w/cm
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Minimum water, paste volume – Effect of w/cmFor water slump of 1 in. before WR addition
But what if WRA can be added earlier?
0.40 0.47 0.5540% SL 265/28% 260/26% 250/24%
PC 265/26%25% FA 255/26%
40% SL A 240/24%
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Minimum CM content for acceptable performance – Effect of w/cm
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Minimum water, paste volume – Effect of w/cmFor no measurable water slump (use of WRA)
0.40 0.47 0.5540% SL 202/22% 218/22% 230/22%
PC 207/22% 221/22% 235/22%25% FA 199/22% 212/22% 225/22%
40% SL A 203/20%
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Minimum CM content for acceptable performance0.47 w/cm 40% slag mix
Condition Water CM PV, %Control 300 640 30%
Water slump=1 in. 260 550 26%No water slump (NWS) 218 460 22%
NWS - air entrained 203 430 20%
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Benefits of not specifying minimum CMBetter concrete performance
Optimized mixtures
Sustainable construction
Incentive to lower variability, i.e. improve quality
Knowledgeable producers
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How to specify to get low CM content concrete?What if producers reduce CM contents too
low?
What if we state a maximum CM content?
What if we state a maximum paste volume?
What if we state a strength range?
Reasonable performance specs – best solution!
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Thank you
Karthik Obla
Spring 2019 National Concrete Consortium
Denver, CO