Invented by John M. Guynn, Roman Cement LLC
The Roman Cement LLC invention works as followsQuarry powder and/or limestone fines are used to reduce the clinker content of concrete, mortar, and other cementitious materials, usually in conjunction with one or more pozzolanically-active SCMs. A portion of hydraulic cement binder or fine aggregate can be replaced and/or enhanced by limestone powder and/or quarry fines. A portion of the cement binder and fineaggregate can be replaced by quarry fines or limestone powder. They act as an intermediary that fills in the space between the largest and smallest cement particles. Supplemental lime can be used to maintain or increase the calcium ions in the mix water, pore solution and/or mixture. Supplemental sulfate can be used to address sulfate deficiency caused by high clinker, superplasticizers, and SCMs that contain aluminates. This systematic approach to using quarry fines and limestone powder, SCMs and lime, and sulfate can address many issues and allows for high clinker reduction with comparable or higher strength.
Background for Use quarry fines or limestone powder to lower the clinker content in cementitious compositions.
The invention is generally in the field of cementitious compositions, hydraulic cements, blended cements, supplementary cementitious materials, quarry fines, limestone powder, performance-enhancing particulate pre-mixes, and methods of manufacture.
2. Relevant Technology
The cement and concrete industries are constantly looking for ways to replace Ordinary Portland Cement with other materials that are more cost-effective and less carbon-intensive. OPC production generates huge amounts of CO2 and accounts for about 5-7% of all man-made CO2. OPC production releases about a ton CO2 into the atmosphere. The world’s cement production is approximately 4.2 billion tons annually. This means that cement manufacturing produces around 4 billion tons of CO2 each year. Based on the unit cost of cement and the quantity added, cement is also the most expensive component in concrete. It is important to reduce clinker and other cementitious binders, as it lowers CO2 production and costs.
Ground granulated blast furnace slag (GGBFS), flyash, natural pozzolans and silica fume (?supplementary cementitious material)? ?SCMs? SCMs have been used in cement mixtures as well as as concrete substitutes. Blended cement often uses SCMs interground with clinker. Interground blended cements, which are often ground finer than OPC to offset strength loss, are usually interground with clinker. This can make them more reactive, but can also adversely affect concrete durability and water demand. There is a limit on how much clinker can substitute with SCMs, especially in the early stages of strength. SCMs are used widely, but many of the SCMs known, including most of the flyash produced, aren’t used and discarded in the environment or aren’t being developed. SCM utilization is still suboptimal despite the known economic and environmental benefits of reducing clinker content by increasing SCM use. This is due to significant technical hurdles.
To make Portland-limestone cement, limestone was interground with cement cement clinker. Limestone can be ground more easily than cement clinker because it is softer and easier to grind. It forms mainly in the ultrafine fraction. Limestone has no cementitious and pozzolanic qualities so only a limited amount of limestone can be interground in cement without compromising strength, durability, or other performance criteria. ASTM C-150 had not allowed limestone addition to Types I-V cement until recently. In 2003, Hawkins et al. Hawkins et al., of the Portland Cement Association, published a paper titled?The Use of Limestone In Portland Cement: A Review of the State-of-the-Art?. This paper argued for a change to ASTM C-150 that would allow up to 5% limestone to be added to OPC. ASTM C-150 was modified in 2004 to allow limestone additions up to 5% to Types I-V cement. ASTM approved in 2012 a proposal to amend ASTMC-595 (blended cements), to allow the inclusion of 5- to 15% limestone. These standards show that limestone can be used as a substitute to cement clinker. This is in contrast to SCMs like GGBFS or fly ash which are more commonly used in higher amounts than 15%. However, they can contribute to long-term strength (although they often reduce the initial strength). Interground Portland-limestone cement has to be ground finer to prevent serious strength loss. This is why OPC offers little to no economic advantage. Cement companies have a large supply of limestone, and can use it to fill clinker and increase production. This is the main benefit. Customers receive little or no cost savings. OPC can be more expensive than blended cements, which makes them less appealing than OPC due to their lower performance. Intergrinding clinker and natural pozzolan in Mexico can produce blend cement that has excellent pour performance. Technically, the main drawback is the inability of controlling the relative particle sizes (PSDs), of the limestone and cement particles interground. This results in variability and uncertainty in performance.
Researchers have used separate processed ultrafine or fine limestone (sometimes called “nano-limestone”) for their research. To replace cement clinker and to increase strength in high volume fly-ash (HVFA), mortars. In ultra-high performance concrete (UHPC), ultrafine limestone was also used as a mineral filler, similar to silica fume, to reduce pore size and increase the paste density. Ultrafine limestone contains very small particles, with most of them being less than 8 millimeters in size. Ultrafine limestone can be used to increase strength but is often more costly than OPC. It is not economically feasible for concrete and general purpose cements.
Leftover quarry fines, sometimes called rock dust) are a promising source of low-cost limestone and other mineral powders. or?quarry waste products? From aggregate manufacturing. The processing of crushed stone to be used as construction aggregate involves blasting, primary crushing, secondary crushing, washing and screening.
Quarry byproducts are created during crushing and washing operations. The Federal Highway Association (FHWA RD-97-1480), last modified March. There are three main types of quarry byproducts that result from these operations: screenings and pond fines.
?Screenings? The finer fraction of crushed rock that remains after secondary and primary crushing, and subsequent separation using a 4.75mm (No. 4) sieve. 4) Sieve. Screenings are made from freshly fractured rock and have a uniform gradation. They also don’t usually contain large amounts of plastic fines. Screenings consist of finely sized, sandy material that has some silt particles. Screenings can range in particle size from 3.2mm (???? inch) to a finer than 75 % (No. Screenings can range in particle size from 3.2 mm (???? inch) to 75?m. 200 sieve). The normal percentage of particles smaller than 75 mm is 10% by weight. Some particles as small as 4.75mm (No. The screen size used to separate the particles is 4 sieve. Screenings from certain processing operations may contain weathered or overburden materials.
?Settling fines in ponds?” The fines from washing crushed stone aggregate. The coarser sizes (greater than No. A sand screw classifier can be used to recover the 30 sieve from washing. The overflow of fines is then discharged into a series of settling ponds. Sometimes, they are also treated with flocculating chemicals. ?Pond clay? It is used to refer to waste fines that are derived from washing natural sands or gravels. When pond fines are initially recovered from the water, they consist of a fine-grained, low-solids slurry with 90-95% of particles smaller than 150 mm (No. 100 sieve and 80% finer than 75?m.
?Baghouse fines? Because of the lack of demand for washed aggregate products or dry climatic conditions, they are made in quarries that are considered dry plants. To capture the dusts from crushing operations, dry plant operation will require dust collection systems such as baghouses and cyclones. These fines are known as baghouse dust. Particle sizing can vary with fines made from different types or stones, but the range of particle sizes is 75?m (No. 200 sieve) to 1 mm or finer. Baghouse fines can also be used as a source for?nanolimestone. When milled to an average particle size of 1-8?m or more
It is estimated that at least 159 million tonnes (175 million tons), of quarry byproducts are produced each year in the United States. Most of these products are made from crushed stone production operations. The U.S. may have accumulated as much as 3.6 million metric tons (4 trillion tons) of quarry products. FHWA-RD97-1480 states that it is possible to use very few of the 159 millions metric tons (175,000,000 tons) of quarry by-products produced each year, particularly pond fines. Three states, Arizona, Illinois, Missouri, and Vermont, indicated in a survey that quarry byproducts were used as embankment materials. Three other states, Florida, Georgia, Vermont, and Vermont, indicated that they also use quarry byproducts in subbase or base applications. Limestone screenings have been used in agriculture limestone production, while baghouse fines from the quarry were used to fill asphalt paving. Baghouse fines from quarry sources have been milled, classified and/or sorted in limited quantities to produce nano-limestone for laboratory testing. However, they are not used consistently in concrete.
Quarry dust can be used as mine safety dust in coal mines. The danger of mine explosions is created by combustible coal dust. Black lung is also caused by coal dust. in miners. The dusting of coal mines using rock dust helps reduce the risk of explosions. This is done by diluting the combustible mine dust with a noncombustible powder, or by misting water to remove particulates from the air. Non-combustible dust must pass a No. 20 sieve, and at least 50% passing No. 200 sieve. Silica-based dust can be harmful if inhaled. Limestone-based quarry fines (limestone rocks dust) are safer options for mine safety dust. They have low levels of silica. Staker Parson, located in Ogden (Utah), produces and sells limestone-based mine dust. Oldcastle’s division. Staker operates and owns an aggregate quarry, which produces limestone and dolomitic lime aggregates for several of Staker?s ready-mix concrete plants in Utah. The remaining quarry fines are then collected and further processed, which is sold to the coal mine operators. Other companies make similar products, including Graymont, Blue Mountain Minerals and E. Dillon & Company. Omya, Carmeuse and Carmeuse. Concrete companies do not use quarry fines in their concrete production, despite the fact that they are made by concrete companies and aggregate producers. They are also readily available in the same places as concrete aggregates, which are very abundant, and retail at around $2-$8 per ton in bulk.
The reason concrete and cement industries failed to use quarry fines in concrete is because they unpredictably and negatively increase water demand. They also negatively and unpredictably impact rheology (flow) and workability properties. W.R. Grace published a paper entitled “Use Chemical Admixtures to Modify The Rheological Behavior Of Cementitious Systems Containing Made Aggregates.” 2010 Concrete Sustainability Conference, National Ready Mixed Concrete Association. (Grace Article). The Grace Article described the unpredictable and negative effects of quarry dust on concrete’s rheology, and suggested that increasing cement and/or SCM levels is the best way to mitigate these effects. The Grace Article stated that quarry fines are used to make sustainable concrete using locally-produced materials, despite the detrimental effects on concrete. Concrete that is made with more cement can be less durable. The Grace Article also explored the undesired interaction between polycarboxylate-based superplasticizers and clay-bearing aggregates containing high quantities of quarry fines. The Grace Article addressed this issue by examining the interaction between natural and manufactured sands and a bio-polymer-type viscosity-modifying agents (VMA), which is a class admixture that’s used with angular-shaped fine aggregates. A company that was trying to find an additive for quarry fines abandoned the project because of a lack of interest or failure from the concrete industry.
Quarry fines cannot be used as concrete additives because they are not compatible with any specific category of concrete materials. Concrete companies and researchers have only two options: to use quarry fines to replace or augment OPC, or as an aggregate. Quarries fines are not like other SCMs and can be even finer than fine aggregates. This means that their effects on strength and rheology can be unpredictable and often negative. At an academic cement conference held in November 2017, the following question was posed: “What is limestone powder?” Is it a cementitious binder? One expert in the field said: “Neither.” The expert in the field replied: “Neither.” He replied, “There isn’t one.” This blind spot in ASTM standards and common practice among experts in this field highlights why it has been difficult, if certainly impossible, to intelligently use quarry fines or limestone powder to make concrete with predictable strength and rheology.
The concrete industry’s inability to use quarry fines effectively is not surprising. Concrete industry requires concrete that meets the requirements of engineers and building codes. This concrete must be predictable and consistent. There is a long-standing, but unmet need to use quarry fines in concrete. Concrete must be stronger and more durable. Despite their high availability, low cost and immense push to produce more sustainable concrete over the past 20 years, cement, concrete and admixture companies have failed to devise a system that is reliable, consistent, and easy to follow. This highlights the problem and the inability to find a solution.
Disclosed are compositions and methods of manufacturing cementitious compositions that include quarry fines or limestone powder. These compositions have predictable water demand, predictable rock rheology, predictable strength, predictable admixture requirements and other performance benefits. An example method comprises mixing together hydraulic cement, quarry fines and/or limestone powder, an aggregate fraction, and water so that the cementitious composition has a ?defined water-to-cementitious binder ratio? (?defined w/cm? (?defined w/cm?) The cost of replacing a portion or all of the cementitious binder with limestone powder and quarry fines can be significantly reduced. However, it will not affect desired strength, water demand, durability, admixture requirements, rheology, and other performance characteristics.
An example cementitious mixture includes hydraulic cement, quarry powder and/or fines (e.g. having a d90 of about 50 m to about 150 m), an aggregate fraction and water. A first portion of quarry fines or limestone powder is considered to be contributing to the cementitious binding agent, while a second portion is considered to form part of aggregate fraction and not to the defined W/cm. A portion of the quarry fines or limestone powder can be considered?cementitious binding agent? Without overstating the impact of quarry fines or limestone powder on water demand, it can reduce clinker content as well as account for the reduction in clinker. You can attribute a portion of the limestone powder and/or quarry fines to the aggregate fraction, e.g. as an ‘ultrafine aggregate. This cement paste fraction contains a portion of the quarry fines and/or limestone powder. It provides strength-enhancing filler effects by increasing the total cement paste fraction, without overstating its impact on strength. Quarry fines and limestone powder can be beneficial in increasing the particle packing density of cement binder particles. This results in a denser cement paste. They also help to reduce drying shrinkage, autogenous and plastic.
There is evidence that cement paste made from quarry fines may bind stronger to coarse aggregates. This is based on the hypothesis that quarry fines can be used to densify cement paste in an interfacial zone (ITZ). The ITZ is where paste strength is at its lowest due to a gradient of decreasing w/cm between bulk paste and the coarse aggregate surface. Further, it is possible that cement particles shrink during hydration, which could cause higher plastic shrinkage in the ITZ. This can lead to microfissures which can reduce paste-aggregate bond strengths and/or create pores which allow for ion transportation. These can adversely affect durability and increase the possibility of chemical attack on the cement paste or the alkali-silica reactions (ASR) at aggregate surfaces. Non-shrinking limestone and quarry fines are thought to be nucleation sites for cement crystal formation. This could significantly increase paste density and decrease paste shrinkage in ITZ. It may also result in a higher bond strength between paste and aggregate and/or better resistance to chemical attack.
In certain embodiments, it may be beneficial to identify a cutoff size between fine quarry fines or limestone powder particles. This can be used to determine the particles as?cement? (or ?cementitious binder?) or ?aggregate? (or ?non-cementitious filler?) Depending on whether they are smaller than or larger than the cutoff particle sizes. To give an example, and not limit it, if 45 m was the cutoff particle size, then quarry fines or limestone particles smaller than 45?m could be assigned or designated as cement? or?cementitious binding agent? Particles larger than 45 mm can be assigned or designated as aggregate. Concrete or cementitious compositions with predictable water demand, strength, and rheology will not include any material that is less than the defined w/cm. It can be determined empirically or arbitrarily or approximated from experience. The cutoff particle size may be any reasonable value that is consistent with the methods. It can range from about 15 m to about 75 m, or about 20 m to about 65 m, or about 25 m and 55 m, or about 30 m or 50 m.Click here to view the patent on Google Patents.