Embodiments relate to cementing operations and, in certain embodiments, to passivated cement accelerators and methods of using passivated cement accelerators in subterranean formations. An embodiment may comprise a method of cementing comprising: providing a cement composition comprising cement, water, and a passivated cement accelerator; and allowing the cement composition to set.

Class C fly ash-based cementitious materials, concretes, and related techniques are disclosed. In accordance with some embodiments, an activated class C fly ash-based cementitious material may be produced by intergrinding class C fly ash (e.g., classified to remove quartz and/or other contaminants and, thus, increase the reactive materials present), an activator, sodium citrate, borax, and a polycarboxylate material. The class C fly ash may have an amorphous glass content of about 60 wt % or more, a calcium oxide (CaO.sub.2) content of about 20 wt % or more, and a quartz content of about 10 wt % or less. The activator may be a chemical which reacts with class C fly ash to form strtlingite structures therein when introduced with water. In some cases, the cementitious material may be provided as an all-in-one powder blend. In some cases, techniques disclosed herein may be utilized in providing a fast-setting flowable fill material.

The present disclosure relates to downhole fluid additives including a clay, a hydroxylated polymer, a cation, and water. The disclosure further relates to downhole fluids, including drilling fluids, spaces, cements, and proppant delivery fluids containing such as downhole fluid additive and methods of using such fluids. The downhole fluid additive may have any of a variety of functions in the downhole fluid and may confer any of a variety of properties upon it, such as salt tolerance or desired viscosities even at high downhole temperatures.

A strength enhancing admixture for cementitious and/or pozzolanic compositions including, based on the total dry weight of the admixture, calcium silicate hydrate in an amount of from about 0.5 to about 94 weight percent, and: i) at least one alkanolamine in an amount of from about 0.5 to about 55 weight percent; ii) at least one inorganic accelerator in an amount of from about 0.5 to about 85 weight percent; and iii) at least one carbohydrate in an amount of from about 0.5 to about 50 weight percent; wherein the calcium silicate hydrate includes a product of a reaction of a water-soluble calcium compound with a water-soluble silicate compound in presence of a water-soluble dispersant; and wherein the at least one inorganic accelerator includes any inorganic accelerator(s) other than calcium silicate hydrate.

A process of preparing a concrete mixture includes the following steps: (a) providing a nano-sized non-sand silica and water; (b) mixing the non-sand silica with the water to form a silica-water mixture; (c) mixing an acid into the silica-water mixture to form a treated water; (d) mixing Portland cement and the treated water for a time sufficient to wet the Portland cement with the treated water to form a Portland/treated-water mixture; (e) mixing aggregate and the Portland-treated-water mixture to form an uncured concrete; and (f) allowing the uncured concrete to cure to form a cured concrete.

Portland cement clinker LCMs that include Portland cement clinker to mitigate or prevent lost circulation in a well. A Portland cement clinker may include Portland cement clinker, Portland cement, a carrier fluid, and an inorganic consolidation activator. Another Portland cement clinker LCM may include Portland cement choker and a crosslinked fluid, such as a polyuronide crosslinked via calcium ions or a polysaccharide crosslinked via divinyl sulfone. Yet another Portland cement clinker may include Portland cement clinker and polymer fibers or particulate glass. Methods of lost circulation control using a Portland cement clinker LCM are also provided.

A cement composition for use in a well that penetrates a subterranean formation comprising: cement; water; and an additive comprising zirconium dioxide, wherein at least a portion of the zirconium dioxide is in a metastable tetragonal phase, and wherein some or all of the zirconium dioxide that is in the metastable tetragonal phase transforms to a stable monoclinic phase after a stress is applied to the cement composition. The additive also reduces the dimensions of a crack located within the set cement composition. A method of cementing in a subterranean formation comprising: introducing a cement composition into the subterranean formation.

A composition and process for manufacture thereof used in hybrid inventive building materials comprising Syngenite (K.sub.2Ca(SO.sub.4).sub.2.H.sub.2O) and Struvite-K (KMgPO.sub.4.6H.sub.2O). Starting constituents include magnesium oxide (MgO), monopotassium phosphate (MKP) and stucco (calcium sulfate hemihydrate), mixed in predetermined ratios, cause reactions to proceed through multiple phases, which reactions variously are proceeding simultaneously and in parallel. Variables, e.g., water temperature, pH, mixing times and rates, have been found to affect resultant reaction products. Preferred ratios of chemical constituents and manufacturing parameters, including predetermined weight percent and specified ratios of Struvite-K and Syngenite are provided for building products used for specified purposes. Reactions are optimized in stoichiometry and additives to reduce the combined heat of formation to non-destructive levels. Various additives help control and guide reactions. Building products, such as board panels, include the resultant composition. A significant amount of the composition is disposed adjacent a building panel face.

The invention provides methods and compositions for treating wash water from concrete production with carbon dioxide. The treated wash water can be reused as mix water in fresh batches of concrete.

The coupled borate/silicate salts-based additive for mortar or concrete controls chloride induced pitting and uniform corrosion of steel rebars embedded in the mortar or concrete with no detrimental effect on compressive strength of mortar/concrete. The silicate compounds may include one or more of the salts of sodium, potassium, lithium, calcium, magnesium, manganese, iron, zinc, aluminum and other transition and valve metals. The borate compounds may include one or more of the salts of alkali and alkaline earth metals, transition, non-transition and valve metals such as sodium, potassium, lithium, calcium, magnesium, manganese, iron, zinc, aluminum and others. The combination of the borate and silicate salts as an additive has been shown to impart high protection to steel rebar surfaces against corrosion, and particularly chloride induced pitting corrosion. The additives are equally effective for mortar as well as concrete. They are also eco-friendly, economical, and are easily applied at construction sites.