New Initiatives in Alkali-based Silicate Cements

Transcription

1 New Initiatives in Alkali-based Silicate Cements Dr. Charles A. Weiss, Jr. Dr. Philip G. Malone US Army Engineer Research and Development Center Vicksburg, MS

2 Introduction Alkali-based silicate cements are special cements formed by mixing a concentrated alkali solution with a finely ground reactive silicate or aluminum silicate ABS cements are strong, fast-setting, inexpensive to made and very versatile Manufactured from glassy silicates (typically metallurgical slags), fly ash and low-fired clays Can use waste alkali Solidified Soil

3 Why Use ABS Cement? Faster--Concrete sets in minutes and gets ultimate strength in days Easy to Obtain --Suitable raw materials are available almost everywhere Economical uses waste materials or low-fired soils Versatile basic chemistry adapts from concrete to soil cement to foamed concrete to expedient patching material

4 Short History of ABS Cements Developed in Belgium in Started as a test for reactivity of slag to be added to conventional cement. Mixture of slag and lye set faster and was stronger than cement. Russians picked up technology in 1950 s and built a 20- story building with no Portland cement in 1990 s Finns built an instant warehouse from F-Cement in 1990 s Lone Star Cement picked up technology from Russians and French in 1980 s and had a good run with blended cement product Currently subject of research in China, Russia, France, Australia

5 Products Have Impressive Performance (1) shrinkage during setting: <0.05%, not measurable. compressive strength (uniaxial): > 90 MPa at 28 days (for high early strength formulation, 20 MPa after 4 hours). flexural strength: MPa at 28 days (for high early strength 10 MPa after 24 hours). Young Modulus: > 2 GPa. freeze-thaw: mass loss < 0.1% (ASTM 4842), strength loss < 5% after 180 cycles. wet-dry: mass loss < 0.1% (ASTM 4843). ph: crushed and powdered, after 5 minutes in deionized water (compared to Portland cement: 12 to 12.5, and granite: 11). leaching in water, after 180 days: K 2 O < 0.015%. setting: 10 hours at -20 C to 7-60 minutes at +20 C. water absorption: < 3%, not related to permeability.

6 Products Have Impressive Performance (2) hydraulic permeability: m/s. Sulfuric acid, 10%: mass loss 0.1% per day. hydrochloric acid 5%: mass loss 1% per day. KOH 50%: mass loss 0.2% per day. ammoniac solution: no mass loss. electrical conductivity: strongly dependent on humidity. sulfate solution: shrinkage 0.02% at 28 days. alkali-aggregate reaction: no expansion after 250 days, -0.01% (compared to Portland Cement with 1% Na 2 O, +1.5%). linear expansion: < /K. heat conductivity: 0.2 to 0.4 W/Km. specific heat: 0.7 to 1.0 kj/kg. thermal stability: mass loss < 5% up to 1000 C. strength loss < 20% at 600 C, < 60% at 1000 C

7 Composites Offer Interesting Possibilities Composite materials have some interesting properties Can be used with metallic, ceramic or synthetic fiber reinforcement Can be used with fabric or discrete fibers

8 Why Hasn t ABS Cement Taken Over the Market? It is NOT Portland cement! No one writes specs for use of non-pc concrete Requires phosphate or borate retarders products used to regulate set with PC will not necessarily work with alkali-based silicates Handling and placing characteristics are slightly different-- uses more vibration-- uses minimum water Si-O-Al-O-Si bond

9 Why Should Military be Interested? Enables use of local materials (ground slags, fly ash, fired clays) in place of and along with conventional Portland cement Durable expedient construction Faster set, higher strength gain Great record for placement in adverse conditions (too hot, too cold) Good product for mobile in-line mixing plant use Offers one-step foaming process for crater repair Alkali for activation, retarders, foamers are all transported as dry powder minimum logistical requirement All components have indefinite shelf life no overaged materials Can use conventional steel reinforcement or synthetic fiber materials Can be used in underwater concreting

10 What are the Military Applications? Expedient paving for roads and runways Hardening of protective structures Roadway-runway repair Soil stabilization Cast-in-place and cast-on-site construction Underwater concreting (portexpansion) Rapid crater in-filling Tough flame-proof construction panels Silioxo Building Panels

11 How Would ABS Class as Leap Ahead Science and Technology? Excellent groundwork in current products Immediately usable technology that can benefit from additional basic research Technology is already used in manufacturing strong light weight panels for use in race cars replaces magnesium metal and fiberglass with strong non-flammable panels Much of the research into microstructure and performances requires sophisticated analytical techniques (nuclear magnetic resonance, or specialized transmission electron microscopy) Advances in basic understanding of molecular structure can pay off in much improved binders for manufacturing and construction

12 Why Will Alkali-Based Cement Work as a Research Area? It relates directly to the Corps Military Mission Enough work has been done to show that there is sound science behind the technology Work from the zeolite research area can be carried over into cements Products (tiles, fireproof panels, pavers) are being produced and can be used as examples of successes Technology has been used in large-scale construction There are a variety of research gaps that the Corps R&D can fill in properties in structures, coatings, retarders, aggregate reactions, chemistry of raw materials (slag, fly ash, fire clays etc.) The material is billed as a cold weather concrete No information found on ballistic characteristics It sells are a green technology

13 Goals Put the Corps Labs at the front of this technology Know more about the material and its application than any other group Work the new materials and products into our construction projects Push the state of the art by looking at a wider range of molecular structures and integrating gel structures, cement formation and zeolite production Work out the relations between the crystalline structures and gel phases that are present

14 How Do We Get Started? Move emphasis is some existing work units to cover the alkali-based cements and related products Start up work units can include this technology Use commercial analytical services (NMR, TEM) until we can build up specialized instrumentation Develop an informal working group to coordinate projects from basic research to evaluation of products Develop an following in the Army using existing products

15 Questions

16 Alkali-slag Patching Material