1. What are VCAS™ Pozzolans?
2. Materials Characteristics of VCAS™ Pozzolans
3. Baseline Cementitious Properties of VCAS™ Pozzolansg
4. Strength Development of VCAS™ Pozzolan Mortars
5. Enhanced Durability through Use of VCAS™ Pozzolans
6. Comparison of VCAS™ Pozzolans with Other Pozzolans
8. Health & Safety
VCAS™ (vitreous calcium aluminosilicate) Pozzolans are new custom-engineered, high performance supplementary cementing materials for use in white Portland cement, mortar, and concrete products. They are manufactured by heating a blend of ground silica, lime, and alumina compounds to a molten state which is then solidified by quench cooling, processed, and ground to a fine white powder with highly-reactive pozzolanic characteristics.
After primary sizing and drying, the feedstock is finely ground and processed through high efficiency classifiers to produce a fine bright white powder with quality assured physical properties. The consistent chemical composition and tightly controlled particle size distribution result in highly reactive and superior quality pozzolans for concrete applications. Currently, the VCAS™ patented technology produces pozzolans in two grades, VCAS-8™ and VCAS-micronHS™, described in this technical summary.
Unlike silica fume, coal fly ash, ground granulated blast furnace slag, and other by-products, VCAS™ Pozzolans are free of iron, manganese, and other undesirable color-inducing impurities, making them ideally suited for all applications using white cement and in pigmented concrete.
VCAS™ Pozzolans are value-added supplementary cementing materials that exhibit pozzolanic activity comparable to silica fume and metakaolin when tested in accordance with ASTM C618 and ASTM C1240. VCAS™ Pozzolans react with calcium hydroxide produced during the hydration of Portland cement to form additional cementitious compounds such as calcium silicate and alumino-silicate hydrates. Pozzolans are widely used in cement and concrete technology to increase concrete strength, density, and resistance to chemical attack as well as control efflorescence.
Notes: VCAS-micronHS™ and VCAS-8™ meet the technical requirements of ASTM C618 for use as supplementary cementing materials in concrete. Blended pozzolanic cements produced with VCAS-micronHS™ and VCAS-8™ also comfortably exceed the requirements of ASTM C1157: Standard Performance Specification for Hydraulic Cement. VCAS-micronHS™ meets the accelerated pozzolanic activity index, ASR control, and sulfate resistance requirements of ASTM C1240 for silica fume.
Notes: The graph top shows the strength development of mortar without pozzolan (control), and mortar with replacement of 20% cement with VCAS-micronHS™ pozzolan. Note that the use of VCAS-micronHS™ pozzolan not only well exceeds the 75% ASTM C618 strength index requirement, but also well exceeds the 28-day strength of the control. VCAS-micronHS™ also exceeds the control strength at 3 days, making it an excellent choice for high performance applications where high early strength is required.
VCAS-8™ Pozzolan meets the strength requirements of ASTM C618 at 7 and 28 days and exhibits excellent long-term strength potential, reaching 113% of the control strength at 90 days.
Tests conducted with a medium alkali Type 1 Portland cement.
Notes: Under the accelerated conditions of ASTM C1240, at 10% Portland cement replacement, it can be seen in the upper graph that VCAS-micronHS™ has performance comparable with silica fume, and VCAS-8™ has performance comparable with metakaolin.
Tests were also conducted in pozzolanic mortars prepared at constant w/c = 0.4, adjusted to standard flow by superplasticizer dosage (lower graph). Mortars with 20% VCAS-micronHS™ develop 131% of the control OPC at 28 days – performance comparable with 10% silica fume, and notably with 40% less plasticizer required for workability.
VCAS-micronHS™ provides an alternative to silica fume with considerably less requirement for costly superplasticizer dosage.
Notes: Using VCAS-micronHS™ (VCAS-3), strength development in the pozzolanic mortars is essentially independent of Portland cement replacement level in the range 10–30%. All VCAS™ mortars in this cement replacement range, meet or exceed the control strength at 3 days and exhibit strengths that are up to 128% of the control at 28 days.
Performance in the pozzolanic mortars is still very good at 40% Portland cement replacement, with strengths that are 107% ofthe control at 7 days and 118% at 28 days.
This provides tremendous versatility in mix design with VCAS™ Pozzolans that is not seen with high water demand pozzolans such as silica fume and metakaolin.
Notes: Depending on the source, the strength development characteristics of white cements can be different from ordinary grey Portland cements.
Pozzolanic cement mortars with 20% VCAS-micronHS™ replace-ment achieve 92% and 105% of the control WPC strength at 7 and 28 days, respectively. Even with 40% VCAS-micronHS™ replace-ment, mortar strengths reach 98% of the control at 28 days.
Note that the 28-day strength of the pozzolanic WPC mortar with VCAS™ is comparable with that produced by the pozzolanic OPC mortar – representing 128% of the OPC control strength. Strengths with WPC at 1 day are typically lower than OPC; but at 7 and 28 days, the strengths are higher.
At 20% VCAS™ replacement, the WPC blend meets the strength requirements for ASTM C1157 HE (high early) cement. At 40% VCAS™ replacement, the WPC blend meets the requirements for ASTM C1157 GU cement.
The production of white Portland cement (WPC) requires significant changes in the mineral feed to the kiln, largely to reduce the iron content responsible for color. As a consequence, the mineralization of the resulting WPC clinker is somewhat different from ordinary grey Portland cement (OPC). It is well known that WPC is inherently unstable when exposed to sulfate service environments, typically found in coastal regions of the southern United States and elsewhere, This has limited the broader use of white concrete to areas and applications not affected by sulfate.
VCAS™ Pozzolans provides white Portland cement with superior resistance to sulfate attack. The graph below shows the excellent dimensional stability of a white cement mortar with 20% VCAS™ Pozzolan replacement tested by ASTM C1012 after over 4 years of exposure. Under these harsh test conditions, the 100% WPC control mortar disintegrated in less than 200 days. The VCAS™ pozzolanic white cement has sulfate resistance comparable with or better than Type V cement.
VCAS™ Pozzolans are also very effective at controlling the deleterious expansion caused by alkali-silica attack in concrete. This can be a particular problem in architectural concretes and precast products that must use light colored or decorative aggregates. Alkali silica attack in concrete involves a delayed reaction between the reactive silicates (e.g. chert, opaline silica) in the aggregate and the alkalis produced by Portland cement hydration. Pozzolans such as VCAS™ are effective at sequestering the aggressive cement alkalis, thereby reducing considerably the attack on the susceptible aggregates.
When tested by the ASTM C441 method, mortars prepared with 20% VCAS-micronHS™ pozzolan replacement typically showed 99% reduction of expansion at 14 days (0.0045 vs. 0.337 for the control). VCAS-8™ pozzolan typically exhibited 85% reduction of expansion at 14 days.
The supplementary cementing reaction of VCAS™ Pozzolans provides increased strength and densification of the cementitious matrix, which has the beneficial effect of significantly reducing the porosity and permeability of concrete. One consequence of this is that concretes incorporating VCAS™ Pozzolans will have reduced chloride ion penetration (ASTM C1202) making them less susceptible to chloride-induced corrosion of embedded reinforcing steel.
In much the same way that the sequestering of cement alkalis reduces alkali-silica attack, VCAS™ Pozzolans are also very effective at reducing both short-term (lime-rich) and long-term (alkali-rich) efflorescence and staining in buildings and structures using white cement concrete. This property will also help the designer and architect achieve better color retention and matching in decorative and colored concretes and mortars used in applications such as cladding panels, roof tiles, swimming pools, terrazzo, and stucco.
The following table compares the properties of VCAS-8™ and VCAS-micronHS™ with other common pozzolans. The white color of VCAS™ Pozzolans is unique among mineral admixtures used for concrete and is found in only a few grades of metakaolin. The second distinguishing feature of the VCAS™ Pozzolans is their low water demand that is in marked contrast with the 10% higher water demand of the other high reactivity pozzolans, silica fume and metakaolin. This low water demand enables the VCAS™ Pozzolans to be used at significantly reduced dosages of chemical admixtures, and/or at much higher cement replacement levels, according to the design goals of the concrete.
The white color, high reactivity, and low water demand make VCAS™ Pozzolans an excellent choice for use with white Portland cement to produce durable, high performance architectural concrete structures and reflective highway barriers.
VCAS™ Pozzolans have an important role to play in sustainable “Green” construction by increasing service life and reducing the net greenhouse gas emissions (GHG) and energy consumption for a cubic yard of concrete. For every ton of cement replaced by pozzolan, there will be a net reduction of about 0.86 tons of carbon dioxide released to the atmosphere and about 4.3-million BTUs of energy consumed. To put this in perspective, every 7 tons of VCAS™ Pozzolan used is the equivalent of taking one car off the road as far as carbon dioxide emissions; and every 49 tons pozzolan sold saves enough BTUs to heat one home for a year. Also, when one ton of a pozzolan is used, it saves about 1.5 tons of virgin material required to make one ton of cement.
The LEED (Leadership in Energy and Environmental Design) Green Building Rating System® is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings.
Many cities and government agencies require LEED certification for new public buildings. Improving the durability of concrete with recycled content reclaimed from local/regional sources and reducing heat island effects with the use of light-colored/high reflectivity materials help earning LEED points toward achieving a greater level of LEED certification.
VCAS™ Pozzolans are non-toxic, contain no crystalline silica, and are classed as nuisance dust, in common with other common fine particulate industrial minerals.
“White Pozzolan Composition and Blended Cements Containing Same,” US Patent No. 6,776,838, Aug. 17, 2004. Copy appended.
“White Pozzolan Composition and Blended Cements Containing Same,” US Patent Application No. 2004/0250736, Dec. 16, 2004. Pending.
“White Pozzolan Composition and Blended Cements Containing Same,” PCT / International Application, No. WO 02/070424 A1, Sept. 12, 2002. Pending.