Zeolite in the Production of Concrete
Zeolite is a suitable raw material in the production of concrete and can partially replace Portland cement in cement blends. Zeolite reduces chloride permeability and expansion due to alkali-aggregate reaction, while improving resistance to acid and sulphate attacks.
The use of natural zeolites as pozzolanic materials in construction dates back 3000 years, to the Greek and Roman periods when zeolites, occurring as altered volcanic ash, tuff, and trass, were used with lime in mortars and concretes for construction. The Romans used Neapolitan Yellow Tuff zeolites near Pozzuoli. Italy used it in the construction of aqueducts, public buildings, and highways. The lime and zeolite combination showed excellent cementitious properties. Natural zeolite tuffs have been used for many years as cement pozzolans in Serbia, Germany, Italy, Bulgaria, China, and Russia.
Despite their widespread applications in pollution control, energy conservation, agricultural, mining, and metallurgical applications during the last few decades: the construction industry appears to be the largest natural zeolite end-user. Worldwide the estimated total natural zeolite production of 3.6 metric tons per year in 2004, construction industry appears to consume about 2.4 metric tons per year, where the bulk of the production is in dimension stones used in building construction and lesser amounts in lightweight aggregate concrete and as pozzolans in concrete.
The use of zeolites in the US concrete industry still lags behind the rest of the world
Approximately 50,000 tons per year of zeolitic tuff is being used for the production of Portland pozzolan cement in Germany. Italy consumes yearly about 3 million tons and China about 5 million tons of zeolitic tuffs as a component of blended Portland cement. The use of natural zeolite as a pozzolan in the US cement and concrete industry, though not recent, however, is still limited. As early as 1912, the Monolith Portland Cement Company used zeolitic ash-flow tuffs from Tehachapi, California for use as a pozzolan at a 25% Portland cement replacement level to build the 400-km Los Angeles aqueduct.
Despite their inherent crystalline nature, the fine size and higher surface area of the natural sedimentary zeolites plus their strong cation exchange capacity make them a suitable pozzolan in cement. Zeolites consume the calcium hydroxide component of Portland cement hydration by the base exchange process and form cementitious products. Pozzolanic characteristics of many natural fine crystalline zeolites are easily comparable to or, in some instances, even better than their aluminosilicate “glassy” rivals such as fly ash, or ground granulated blast furnace slag.
The present study provides a comprehensive laboratory investigation of the effects of incorporation of clinoptilolite [(Na4K4)(Al8Si40O96).24H2O], a common natural sedimentary zeolite in the western United States as a pozzolan at various levels of substitutions of Portland cement (from 0 to 40 percent by mass of total cementitious materials) on the properties of fresh and hardened concrete and on concrete durability (e.g., alkali-aggregate reaction, drying shrinkage, chloride permeability, and resistance to acid and sulphate attacks). Clinoptilolite used in this study came from a tuffaceous lacustrine deposit, Bear River Zeolite (BRZ), located 10 km from Preston, Idaho, and owned by the Bear River Zeolite Company. A wholly-owned subsidiary of U.S. Antimony Corporation, the company produces clinoptilolite from a green zeolitized tuff in the Eocene Salt Lake Formation that crops out over a large area in southeastern Idaho. The deposit occurs in a very fine crystalline form and has been supplied for this study in its natural state after mining as “fugitive dust” from crushing with no calcining or other processing operations.
A trial by Sedlmajer examined the properties of concrete containing natural zeolite as an active admixture in concrete. The researchers composed individual concrete mixes based on gradual increases in the substitution of Portland cement with natural zeolite.
All admixtures (containing zeolite) were compared to a reference concrete where only Portland cement was used. The dosage of zeolite, which contained 45 percent clinoptilolite and 35 percent of an amorphous phase, ranged from 7.5 – 30 percent of the mass of the cement. The results indicated that zeolite is an active admixture that contributes to the formation of microstructure and to the improvement of required properties of hardened concrete.
Zeolite as a substitute for Portland cement
Sedlmajer concluded that a “finely milled natural zeolite appears to be a suitable raw material in the production of concrete with which it is possible to partially substitute Portland cement."
A paper by Jana examined clinoptilolite zeolite as a pozzolan and replacement to Portland cement in concrete mixtures. Findings indicated that the most significant effects of zeolite are in the reduction of chloride permeability, a significant reduction in expansion due to alkali-aggregate reaction, and an improved resistance to acid and sulphate attacks.
Ahmadi and Shekarchi conducted an experiment that tested the effectiveness of zeolite and silica fume in enhancing the mechanical and durability properties of concrete. They measured both pozzolanic reactivity and the ability to substitute cement in different proportions in concrete mixtures. Experimental tests included slump, compressions strength, water absorption, oxygen performance, chloride diffusion, and electrical resistivity of concrete. Results indicated that concretes containing zeolite improved and were comparable to or better than concretes prepared with silica fume.
Lightweight concrete is produced using a variety of lightweight aggregates like volcanic pumice, clay, fly ash, slate, or shale. It is often used in house construction and applications can include foundation reinforcement, fire resistance, or filling voids in sewer systems, pipelines, and fuel tanks. As developers face increased demands for new materials that are environmentally friendly, studies examine the effects and benefits of natural zeolite in lightweight concrete mixes.
A study by Jitchaiyaphum tested cellular lightweight concrete (CLC) made from preformed foam, Type-I Portland cement, fly ash, or natural zeolite. Properties measured included compressive strength, setting time, water absorption, and microstructure. Results indicated that CLC containing 10wt% of natural zeolite had the highest compressive strength. The replacement of Type-I Portland cement with zeolite decreased the total porosity and air void size but increased the capillary porosity of the CLC. Finally, the incorporation of zeolite decreased the setting time, total porosity, and pore size of the paste compared with mixtures containing the same amount of fly ash.
De Gennaro tested the use of mixtures containing natural zeolites in the production of lightweight concretes. All products and mixtures were tested by means of fusibility and firing tests to evaluate the expanding properties. Results indicated that natural zeolitized materials mixed with DPM (30 wt. %) provide lightweight aggregates with densities ranging between 0.8 and 1.0 g/cm 3 suitable for the preparation of structural lightweight concretes.
Karakurt used clinoptilolite zeolite as an aggregate and bubble-generating agent in aerated concrete production. The researchers examined the effects of particle size, replacement amount, and curing time on aerated concrete properties. Results demonstrated that the use of natural zeolite has a positive effect on the physical and mechanical properties of aerated concrete. The optimal replacement amount was 50 percent; at this rate, the compressive strength, unit weight, and thermal conductivity of aerated concrete were measured as 3.25 MPa, 0.553 kg/dm 3, and 0.1913 W/mK. Researchers concluded that zeolite acts as both an aggregate and bubble-generating agent.
ReferencesClinoptilolite - A promising pozzolan in concrete - Dipayan Jana
Natural zeolite and its application in concrete composite production - Yen Thi Trana, et al.
Possibilities of Utilization Zeolite in Concrete - M. Sedlmajer, et al.
Optimization of Concrete Composition with Addition of Zeolite Tuff - Markiv, et al.
A Much Better Concrete with Zeolite Additions - State of the Art Review - Juan Carlos de la Cruz, et al.
An experimental study on durability properties of concrete containing zeolite as a highly reactive natural pozzolan - Meysam Najimi, et al.
Utilization of natural zeolite in aerated concrete production - Cenk Karakurt, et al.
Cellular lightweight concrete containing high-calcium fly ash and natural zeolite - Khamphee Jitchaiyaphum
Market Development and Business Growth Strategy for Light Weight Zeolite Concrete - Hogg