Concrete: Mixing and Testing CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 1 of 35
Objectives • Learn the ASTM Standard for hand mixing • Understanding the time dependency of concrete properties • Learn how to conduct the mechanical and durability testing • Learn the effects of fly ash • Effects of w/c on workability, electrical measurements, and strength • Learn the principles of isothermal calorimeter testing • Learn an application of Power’s Gel Space Ratio Theory CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 2 of 35
Outline • Mixtures • Sample Preparation • Mixing & Placement • Conditioning • Hardened Testing Procedures • Calorimetry Testing • Powers Model • Report CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 3 of 35
Mixtures w/c=0.36 We will distribute the data for these mixtures w/c=0.36, 40 % Fly Ash w/c = 0.3 w/c=0.3 w/o WRA You will make these w/c=0.36 mixtures in the lab w/c=0.42 w/c=0.6 Mixtures are 30% fine aggregate, 30% coarse aggregate by volume There will be a water reducing admixture as well CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 4 of 35
Materials Abs = 1.8 % Abs = 0.8 % We will use oven dry aggregate and increase the mix water to correct for absorption CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 5 of 35
Sample Preparation Prepare a label with your lab section and mixture number CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 6 of 35
Mixing Procedure 1. Assemble Mixing Equipment We will be utilizing the hand-mixing procedure described in ASTM C192 CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 7 of 35
Mixing Procedure 2. Measure materials with the mixture design your group is given in class. 3. Mix cement and fine aggregate We will be utilizing the hand-mixing procedure described in ASTM C192 CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 8 of 35
Mixing Procedure 4. Mix in the coarse aggregate 5. Slowly mix in the water and chemical admixtures We will be utilizing the hand-mixing procedure described in ASTM C192 CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 9 of 35
Placing Procedure • Fill your 3x6 cylinders in 3 equal layers, rod each 25 times • Each group should make 3 — 3x6s • Clean and dispose of excess materials CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 10 of 35
Compression Testing w/ Friction CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 11 of 35
Compression Testing w/o Friction We will use neoprene caps smooth the ends and ensure uniform stress CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 12 of 35
Compression Testing ′ = 𝐐 𝒈 𝒅 𝐁 A is cross-sectional area We are using a 3” diameter cylinder Forney 700 kip compression machine in Pankow Laboratory CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 13 of 35
Electrical Resistivity Testing An upcoming and popular rapid test to give an indication of durability 𝝇 = 𝐒𝐥 This is 𝐒 ! Geometry Factor Electrical (A/L) Resistivity Resistance (measured in lab) CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 14 of 35
Electrical Resistivity Resistivity is a measure of electrical resistance independent of geometry, units of ohm-m ( Ω ∙ m ) Concrete is a porous composite • Solid Phase (reactancts, products, and aggregates) 𝜍 𝑡𝑝𝑚𝑗𝑒𝑡 ≈ 10 9 Ω ∙ m • Vapor Phase 𝜍 𝑤𝑏𝑞𝑝𝑠 ≈ 10 15 Ω ∙ m • Liquid Phase (pore solution) 𝜍 𝑚𝑗𝑟𝑣𝑗𝑒 < 1 Ω ∙ m Electricity is conducted primarily through the liquid Weiss (‘05), Rajabipour (‘06) CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 15 of 35
Electrical Resistivity 𝟐 𝝇 = 𝝇 𝟏 𝝔𝜸 = 𝝇 𝒑 𝐆 𝝇 𝒄𝒗𝒎𝒍 : resistivity (easily measured) 𝝇 𝟏 : pore solution (model/experimental data) 𝝔 : liquid volume fraction Weiss (‘05), Rajabipour (‘06) 𝜸 : connectivity(related to pore distribution) 𝐆 : Formation Factor These parameters can be used to quantify the durability of a mixture These tests are highly dependent on moisture content and temperature! CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 16 of 35
Formation Factor Deicing Salt Deicing salts -> pavements and bridge decks Salt (Cl-) and steel = corrosion Cover We need to know how the Cl- moves through the concrete Main parameter is the “Diffusion Reinforcing Coefficient” which describes the Bar speed Nernst-Einstein D = 1 𝐺 ∙ 𝑑𝑝𝑜𝑡𝑢𝑏𝑜𝑢 CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 17 of 35
Formation Factor The diffusion coefficient can be used to estimate the time to reach a critical concentration level 𝐷 𝑦,𝑢 : 𝐷 𝑦,𝑢 − 𝐷 𝑝 𝑦 = 1 − erf 𝐷 𝑡 − 𝐷 𝑝 2 𝐸𝑢 (with a few assumptions that you will discuss later in the semester) Steel depassivation and corrosion can begin when this reaches a critical level CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 18 of 35
Cement hydration CE530 slides Cement hydration is an exothermic reaction. CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 19 of 35
Five stages in cement hydration by heat CE 530 slides CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 20 of 35
Isothermal calorimetry • A good method for the study of cement hydration process. • Relevant standards include ASTM C186 and ASTM C1702 • Widely used for studying the reaction kinetics of pure cement pastes as well as the temperature dependence of the reaction. • Degree of hydration can be determined by calorimetry. • Q(max) is determined from the chemical composition of the materials For the raw materials in this lab: Q(max) cement: 512 J/g cement CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 21 of 35
Heat flow and cumulative heat 300 3 Cumulative Heat (J/g) 250 2.5 Heat flow (mw/g) 200 2 1.5 150 1 100 0.5 50 0 0 0 50 100 150 200 0 50 100 150 200 Age (hour) Age (hour) In general one test generates two plots: heat flow and cumulative heat. They are intrinsically the same data. Cumulative heat is an integral of heat flow on time. CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 22 of 35
TAM air 8 samples in total CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 23 of 35
Ampoules CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 24 of 35
Powers Model A simple yet effective model that can be used to describe the microstructure of hydrating cement Inputs water-cement ratio ( 𝑥/𝑑 ) degree of hydration ( 𝛽 ) This is an example for a w/c=0.5 CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 25 of 35
Powers Model - Calculations You can program the equations or use spreadsheet on website CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 26 of 35
Report • Three weeks of lab work will be in this report • Worth twice as much as previous write-ups • Sections – Executive Summary (15 %) – Introduction and Background (10 %) – Materials and Methods (10 %) – Results and Discussion (50 %) – Summary and Conclusions (15 %) CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 27 of 35
Report Introduction and Background – Brief description of the main concepts being investigated – Present appropriate equations and/or figures – Use sources such as books, lecture notes, etc and cite them! Remember , It Is About Concept And Theory, NOT Lab Procedure Or Results! CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 28 of 35
Report Materials and Methods – What materials did we use? Be specific – Describe the following procedures in your own words: Mixing Strength Testing Electrical Testing Isothermal Calorimetry CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 29 of 35
Report Materials and Methods – What materials did we use? Be specific – Describe the following procedures in your own words: Mixing Strength Testing Electrical Testing Isothermal Calorimetry CE 331 – Engineering Materials II Slides developed by Spragg, Cao, and Weiss Slide 30 of 35
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