Mechanical Properties of High- Volume SCM Concretes Guðmundur Marteinn Hannesson Dawn Lehman Katherine Kuder Charles Roeder Jeffrey Berman

Overview Project Motivation Introduction Prior Research Research Significance Material and Mix Design Results Analytical Expressions Conclusions Future Work

Project Motivation Reducing the embedded carbon content of the concrete High CO 2 emission associated with concrete production due to high Portland Cement (PC) demand – Ton PC  Ton CO 2 emitted – Replace cement with Supplementary Cementitious Materials (SCMs) Goal is to develop Low PC (80-90% SCM) SCC that is suitable for composite systems

Introduction Hydraulic Reaction Pozzolanic Reaction Some CH (usually PC) needed to efficiently use SCMs fast slow Calcium Silicate Hydrate (C–S- H) Contributes to strength Calcium Silicate Hydrate (C–S- H) Contributes to strength Calcium Hydroxide (CH) does not contribute to strength CH increases durability issues Calcium Hydroxide (CH) does not contribute to strength CH increases durability issues Cement Chemistry Notation: C=CaO, S =SiO 2, H = H 2 O

Introduction Reduces the amount of Portland cement – Decreases the CO 2 emissions Use of waste materials that would otherwise be landfilled Improves both durability and the interface with aggregate Reduces porosity in the concrete Increases workability – Fly Ash as SCM Pros Cons Slow strength gain – low early strength Material variability Time of set Hazardous waste?

Prior Research Considerable research has been done on SCM concrete The focus has been finding the optimum amount of SCM – To obtain maximum strength – Improve concrete Most studies focus on the use of fly ash, although slag has also been investigated

Prior Research Typical SCM percentage levels are between 20-50%, rarely exceed 60%

Research Significance Not many researchers have examined SCC with high volume of SCM This research focus on strength behavior, rather than maximizing strength (some of the SCM can serve as filler) Correlation between replacement, strength and SCM's chemical compositions was examined

Material and Mix Design 5 cementitious materials used for specified concrete mixes – ASTM I Portland Lafarge Cement – Two fly ash: Boardman fly ash (ASTM Class C) Centralia fly ash (ASTM Class F) – Two slag: Seattle slag (grade 100) St. Mary’s slag (grade 100)

Material and Mix Design Compounds Shorthand notation ASTM Type I Boardman FA Centralia FA Seattle SL St. Mary's SL SiO 2 S Al 2 O 3 A Fe 2 O 3 F K 2 O + Na 2 OK+N SO CaOC MgOM Loss on IgnitionLOI Specific gravity (g/cm 3 )SG Active SiO 2 (%)γ Activity Index, 7 day (%)7 AI Activity Index, 28 day (%)28 AI Long-Term Strength Development Early Strength Development Slag has higher percentage of active silica than fly ash

Material and Mix Design Research was performed in two phases: – First phase Four different SCMs: two fly ash and two slag Only binary mixes (cement and one SCM) Replacement levels: 20%, 40%, 60%, 80% and 100% w/b = 0.35 – Second phase Two different SCMs: fly ash and slag Binary and ternary mixes (cement and two SCMs) Ternary mixes made the three different fly ash to slag ratios Replacement levels: 60%, 80% and 90% w/b = 0.40

Material and Mix Design Phase IPhase II Binder (kg/m 3 ) Water (kg/m 3 )167.9 Sand, SSD (kg/m 3 ) Aggregate 3/8 (kg/m 3 )819.5 Sika 2100 (L/m 3 ) w/b Both mix design were intended to have the same mix proportions However, slight oversight in the mix design lead to change in binder content

Overview of Testing Program Phase I (w/b = 0.35) – Compressive strength – Initial time of setting Phase II (w/b = 0.40) – Compressive strength – Elastic modulus – Creep and Shrinkage strains

Time of Set (w/b = 0.35) Decrease in time of set at higher replacements Flash set due to low concentration of gypsum

Compressive strength of Phase I (w/b = 0.35)

Compressive Strength – FlyAsh (w/b = 0.35)

Compressive Strength – Slag (w/b = 0.35)

Compressive strength of Phase II (w/b = 0.40)

Compressive strength – 60% (w/b = 0.40)

Compressive strength – 80% (w/b = 0.40)

Compressive strength – 90% (w/b = 0.40)

Compressive strength – Ternary mixes (w/b = 0.40)

Elastic Modulus

Elastic modulus – Ternary mixes (w/b = 0.40)

Creep Behavior

Creep Strains (w/b = 0.40) Only four creep rigs available Two concrete mixes tested for creep behavior – 90% 50FA-50SL mix – Base II mix Creep RigMix name Day of Loading Stress (MPa) Strength 1 (MPa) Stress/ Strength 190% 50FA-50SL–II % 50FA-50SL–II % 50FA-50SL–II Base II Compressive strength at day of loading

Creep Strains (w/b = 0.40)

Analytical Expressions σ0σ0 E0E0 E1E1 τ σ0σ0

Compressive Strength – Modified Bolomey equation – Total binder chemical composition related to equivalent cement content Elastic Modulus – Evaluated ACI and CEB expressions Creep Behavior – Combined Maxwell and Bingham rheological model

Efficiency Concept Bolomey Strength Equation Modified Bolomey Strength equation Where K B (t) = Bolomey Coefficient a(t) = constant often taken as 0.5 c = Cement content (kg/m 3 ) w = Water content (kg/m 3 ) Where k(t,%) = efficiency factor P = SCM content (kg/m 3 ) Effective w/b = w/(c+kP) Equivalent cement = kP k = 1  SCM is acting as Cement

Compressive Strength vs. C/(S+A)

Equivalent cement content (kp) vs C/(S+A)

Proposed Efficiency Equation

Calculated vs. Measured Strength – using proposed efficiency equation

ACI vs. CEB

Rheological Model σ0σ0 E0E0 E1E1 τ σ0σ0 Day of loading Concrete Cylinder E 0 (GPa) E 1 (GPa) τ (day) E 0 + E 1 (GPa) E - test (GPa) 7SCM Unsealed Sealed SCM Unsealed Sealed SCM Unsealed Sealed Base II Unsealed Sealed E 0 + E 1 = instantaneous Modulus E 0 = Modulus at time infinity τ = Relaxation time (days) σ 0 = The constant applied load t = time since load is applied

Rheological Model

Conclusions

Conclusions – Compressive Strength Early strength (≤ 14 days) typically lower than the base mix Long-term strength is comparable to the base mix Ternary mixes had more reliable strength than the binary mixes Using the proposed efficiency equation gives good first approximation for the SCM’s efficiency

Conclusions – Elastic Modulus The elastic modulus of the base mix was independent of time Ternary mixes had on average 40% increase in modulus from 7 to 112 days The ternary mixes had comparable elastic modulus to the base mix at age 56 days The expression from CEB does better job than ACI of approximating the elastic modulus in this research program

Conclusions - Creep The creep strains of the sealed cylinders were lower than the unsealed cylinders The creep behavior of the SCM mix loaded after 28 days was similar to the base mix loaded after 7 days The rheological model can predict different creep behavior for different loads – Needs experimental data to calibrate the material coefficients

Future Work Test more SCMs at different w/b ratios Test mix with different cement replacement for creep behavior Test mix for creep behavior under higher gravity loads Test high volume SCM concrete mix in a full scale specimen in a composite system

Questions?