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BENEFITS AND ADVANTAGES OF THE NATURAL POZZOLAN
Lithification: Once the Natural pozzolan-lime mixture is hydrated, the pozzolanic reaction begins immediately and continues for many years. Eventually, the mass will reach complete lithification, forming a rocky material similar to plagioclase with some content of magnetite. The compressive strength as well as the flexural strength will continue to increase for a long time. This unique characteristic is one of the main reasons many great ancient structures have lasted for over two thousand years.
Autogenous Healing: A unique characteristic of Natural pozzolan is its inherent ability to actually heal or re-cement cracks within the concrete by means of the continuation of pozzolanic reaction with the calcium hydroxide freed from the cement hydration reaction. This results in the filling up of most of the gaps inside the hardened concrete matrix
Reduced Permeability and Voids: The leaching of water-soluble calcium hydroxide produced by the hydration of Portland cement can be a significant contributor to the formation of voids. The amount of "water of convenience" used to make the concrete workable during the placing process creates permeable voids in the hardened mass. Natural pozzolan can increase the fluidity of concrete without "water of convenience," so that the size and number of capillary pores created by the use of too much water can be minimized.
Reduces Expansion and Heat of Hydration: Experiments show that replacing 30% Portland cement with Natural pozzolan can reduce the expansion and heat of hydration to as low as 40% of normal. This may be because there is no heat produced when Natural pozzolan reacts with calcium hydroxide and that the free calcium oxide in the cement can hydrate with natural pozzolan to form C-S-H. Natural pozzolan decreases the heat generated by cement hydration and delays the time of peak temperature. The graphic pattern of Natural pozzolan - Portland cement mixture is extended longer and lower to form a much more moderate curve than the heat of hydration curve of Portland cement itself.
Reduces Creep and Cracks: While concrete is hardening, the "water of convenience" dries away. The surface of the hardening mass then begins to shrink as the temperature goes down from outside. This results in the formation of creep and cracks. Natural pozzolan moderates the expansion and shrinkage of concrete. It also helps to lower the water content of the fresh concrete. Therefore, the creep and cracks can be significantly reduced without the process of water cooling.
Reduces Microcracking: The expansion and shrinkage mentioned above also create microcracks inside the hardened C-S-H paste and in-between the aggregate and the C-S-H paste. These microcracks significantly contribute to concrete permeability as well as other concrete defects. The Natural pozzolan- Portland cement mixture expands these shrinks so moderately that there is no microcracking inside the C-S-H paste after drying.
Increases Compressive Strength: The pozzolanic reaction between natural pozzolan and calcium hydroxide happens after the C3S and C2S in the cement begins to hydrate. At the early stage of curing, 30% Natural pozzolan substituting Portland cement mixture is slightly lower than reference OPC [Ordinary Portland Cement} in regard to compressive strength. As time goes by, natural pozzolan continues to react with the calcium hydroxide produced by cement hydration and increases the compressive strength by producing additional C-S-H. After 21 curing days, the 30% Natural pozzolan/ 70% Portland cement mixture begins to exceed reference OPC in compressive strength. After 28 days, it exceeds reference OPC by about 15%. The pozzolanic reaction continues until there is no free calcium hydroxide available in the mass and the compressive strength exceeds the reference OPC by 30-40%.
Increases Resistance to chloride Attack: Concrete deterioration caused by the penetration of chloride occurs quickly when chloride ions react with calcium. The expansion of hydrated calcium oxy-chloride enlarges the microcracks and increases the permeablity that causes quicker chloride penetration and more damage from freezing and thawing action. The 30% Natural pozzolan added into cement can react with almost all the free calcium hydroxide and form a much denser past. Thus, the penetration of chloride can be minimized and the few penetrated chloride ions cannot find free calcium hydroxide with which to react.
Increases resistance to sulfate attack: There are three chemical reactions involved in sulfate attack on concrete: 1) Combination of free calcium hydroxide and sulfate to form gypsum (CaSO4-2H2O). 2) Combination of gypsum and calcium aluminate hydrate (C-A-H) to form ettringite (C3A-3CaSO-32H2O). 3) Combination of gypsum and calcium carbonate with C-S-H to form thaumasite (CaCO3-CaSiO3-CaSO4-15H2O).
All these reactions result in the expansion and disruption of concrete. Thaumasite in particular is accompanied by a very severe damaging effect which is able to transform hardened concrete into a pulpy mass.
Reduces alkali-aggregate reaction: Because Natural pozzolan is shattered into such a fine particle size resulting in dramatically increased reactive surface area, it can react quickly with calcium hydroxide and can trap the alkali inside the cement paste. Thus, it helps to form a denser paste with almost no alkali aggregate reaction at all.
Protects steel reinforcement from corrosion: The preceding discussions make it very clear that concrete made from 30% Natural pozzolan/ 70% Portland cement mixture can protect steel reinforcement because it creates an environment so densely packed that no liquids or gases can penetrate through it to cause corrosion to the steel.
Increases abrasion resistance: Natural pozzolan increases the compressive strength of concrete and makes the concrete matrix stronger and more dense. It also prevents the formation of pulpy, crispy, or water-soluble materials created by chemical attack. Therefore, it helps the concrete to durably resist abrasion.
Lowers water requirement with high fluidity, self-leveling, and compression: In normal operations, the bulk volume of concrete in the constructions are placed and compacted by use of high frequency poke vibrators. The rapid vibration induces segregation phenomena of all orders of magnitude in the fresh concrete, e.g., stone segregation, internal bleeding giving bonding failures, and inhomogeneous cement paste and air-void systems. Under proper use of vibratory compaction, Natural Pozzolan minimizes or eliminates these problems due to the amorphous structure of the pozzolan particles.
Improves Durability: The benefits and characteristics of Natural Pozzolan mentioned above clearly explain why the ancient structures built by the Greeks have survived over 2000 years of weathering.
Natural Pozzolan of Nevada