Concrete degradation
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Concrete degradation may have many different causes.
The most destructive agent of concrete structures and components is probably water. Indeed, water often directly participates to chemical reactions as a reagent and is always necessary as a
Corrosion of reinforcement bars
The expansion of the
Concrete, like most consolidated hard
When atmospheric
Formation of expansive phases in concrete
As hard rocks, concrete can withstand high
The most ubiquitous, and best known, expansive phases are probably the
Other deleterious expansive chemical reactions more difficult to characterize and to identify can occur in concrete. They may be first distinguished according to the location where they occur in concrete: inside the aggregates or in the hardened cement paste.
Expansion inside the aggregates
Various types of aggregates can undergo different chemical reactions and swell inside concrete, leading to damaging expansive phenomena.
- Alkali–silica reaction
The most common are those containing reactive
2SiO
3), a strong desiccant with a high affinity for water. This reaction is at the core of the alkali–silica reaction
- 2 NaOH + SiO2 → Na2SiO3 · H2O
Following this reaction, a
A quite similar reaction (alkali-silicate reaction) can occur when
- Alkali–carbonate reaction
With some aggregates containing
(CO2−3). The resulting expansion caused by the swelling of brucite can cause destruction of the material:
- CaMg(CO3)2 + 2 NaOH → Mg(OH)2 + CaCO3 + Na2CO3
Often the alkali–silicate reaction and the dedolomitization reaction are masked by a much more severe alkali–silica reaction dominating the deleterious effects. Because the alkali-carbonate reaction (ACR) is often thwarted by a coexisting ASR reaction, it explains why ACR is no longer considered to be a major detrimental reaction.
- Pyrite oxidation
Far less common are degradation and pop-outs caused by the presence of
2O
3), iron oxy-hydroxides (FeO(OH), or Fe
2O
3·nH
2O) and mildly soluble gypsum
4·2H
2O).
When complete (i.e., when all Fe2+
ions are also oxidized into less soluble Fe3+
ions), pyrite oxidation can be globally written as follows:
- 2 FeS2 + 7.5 O2 + 4 H2O → Fe2O3 + 4 H2SO4
The sulfuric acid released by pyrite oxidation then reacts with portlandite (Ca(OH
2)) present in the hardened cement paste to give gypsum:
- H2SO4 + Ca(OH)2 → CaSO4 · 2H2O
When concrete is carbonated by atmospheric carbon dioxide (CO2), or if limestone aggregates are used in concrete, H
2SO
4 reacts with calcite (CaCO
3) and water to also form gypsum while releasing CO2 back to the atmosphere:
- H2SO4 + CaCO3 + H2O → CaSO4 · 2H2O + CO2
The
2O
3·nH
2O remain in place around the grains of oxidized pyrite they taint in red-ocre
Expansive chemical reactions inside the hardened cement paste
The
- The delayed ettringite formation (DEF) also known as internal sulfate attack (ISA);
- The external sulfate attack (ESA), and;
- The thaumasite form of sulfate attack (TSA).
These three types of sulfate attack reactions are described into more details in specific sections latter in the text. When the hardened cement paste (HCP) is affected, the detrimental consequences for the structural stability of concrete structures are generally more severe than when aggregates are affected: DEF, ESA and TSA are much more damaging for concrete than ASR and ACR reactions.
A common points to all these various chemical expansive reaction is that they all require water as a reactant and as a reaction medium. The presence of water is always an aggravating factor. Concrete structures immersed in water as dams and bridge piles are therefore particularly sensitive. These reactions are also characterized by slow
Chemical damages
Carbonation
3) while releasing a water molecule in the following reaction:
- CO2 + Ca(OH)2 → CaCO3 + H2O
Exception made of the water molecule, the carbonation reaction is essentially the reverse of the process of calcination of limestone taking place in a cement kiln:
- CaCO3 → CaO + CO2
Carbonation of concrete is a slow and continuous process of atmospheric CO2 diffusing from the outer surface of concrete exposed to air into its mass and chemically reacting with the mineral phases of the hydrated cement paste. Carbonation slows down with increasing diffusion depth.[1]
Carbonation has two antagonist effects for (1) the concrete strength, and (2) its durability:
- The precipitation of mechanical strengthof concrete;
- At the same time carbonation consumes portlandite and therefore decreases the concrete spall. Cracks appear in the concrete cover protecting the rebar against corrosion and constitute preferential pathways for CO2 direct ingress towards the rebar. This accelerates the carbonation reaction and in turn the corrosion process speeds up.
This explain why the carbonation reaction of reinforced concrete is an undesirable process in concrete chemistry. Concrete carbonation can be visually revealed by applying a phenolphthalein solution over the fresh surface of a concrete samples (concrete core, prism, freshly fractured bar). Phenolphthalein is a pH indicator, whose color turns from colorless at pH < 8.5 to pink-fuchsia at pH > 9.5. A violet color indicates still alkaline areas and thus non-carbonated concrete. Carbonated zones favorable for steel corrosion and concrete degradation are colorless.[2][3]
The presence of water in carbonated concrete is necessary to lower the pH of concrete pore water around rebar and to depassivate the carbon steel surface at low pH. Water is central to corrosion processes. Without water, the steel corrosion is very limited and rebar present in dry carbonated concrete structures, or components, not affected by water infiltration do not suffer from significant corrosion.
Chloride attack
The main effect of
Chlorides, particularly calcium chloride, have been used to shorten the setting time of concrete.[4] However, calcium chloride and (to a lesser extent) sodium chloride have been shown to leach calcium hydroxide and cause chemical changes in Portland cement, leading to loss of strength,[5] as well as attacking the steel reinforcement present in most concrete. The ten-storey Queen Elizabeth hospital in Kota Kinabalu contained a high percentage of chloride causing early failure.
Alkali–silica reaction (ASR)
The alkali–silica reaction (ASR) is a deleterious chemical reaction between the alkali (Na
2O and K
2O), dissolved in concrete pore water as NaOH and KOH, with reactive amorphous (non-crystalline) siliceous aggregates in the presence of moisture. The simplest way to write the reaction in a stylized manner is the following (other representations also exist):
- 2 NaOH + SiO2 → Na2SiO3 · H2O (young N-S-H gel)
This reaction produces a gel-like substance of sodium silicate (Na
2SiO
3 • n H
2O), also noted Na
2H
2SiO
4 • n H
2O, or N-S-H (sodium silicate hydrate). This hygroscopic gel swells inside the affected reactive aggregates which expand and crack. In its turn, it causes concrete expansion. If concrete is heavily reinforced, it can first cause some prestressing effect before cracking and damaging the structure. ASR affects the aggregates and is recognizable by cracked aggregates. It does not directly affect the hardened cement paste (HCP).
Delayed ettringite formation (DEF, or ISA)
When the temperature of concrete exceeds 65 °C for too long a time at an early age, the crystallization of ettringite (AFt) does not occur because of its higher solubility at elevated temperature and the then less soluble mono-sulfate (AFm) is formed. After dissipation of the cement hydration heat, temperature goes back to ambient and the temperature curves of the solubilities of AFt and AFm phases cross over. The mono-sulfate (AFm) now more soluble at low temperature slowly dissolves to recrystallize as the less soluble ettringite (AFt). AFt crystal structure hosts more water molecules than AFm. So, AFt has a higher molar volume than AFm because of its 32 H2O molecules. During months, or years, after young concrete cooling, AFt crystallizes very slowly as small acicular needles and can exert a considerable crystallization pressure on the surrounding hardened cement paste (HCP). This leads to the expansion of concrete, to its cracking, and it can ultimately lead to the ruin of the affected structure. The characteristic feature of delayed ettringite formation (DEF) is a random honeycomb cracking pattern similar to this of the alkali-silica reaction (ASR). In fact, this typical crack pattern is common to all expansive internal reactions and also to restrained shrinkage where a rigid substrate or a dense rebar network prevents the movements of a superficial concrete layer. DEF is also known as internal sulfate attack (ISA). External sulfate attack (ESA) also involves ettringite (AFt) formation and deleterious expansion with the same harmful symptoms but requires an external source of sulfate anions in the surrounding terrains or environment. To avoid DEF or ISA reactions, the best way is to use a low C3A (tri-calcium aluminate) cement precluding the formation of ettringite (AFt). Sulfate resisting (SR) cements have also a low content in Al2O3. DEF, or ISA, only affects the hardened cement paste (HCP) and leaves intact the aggregates.
DEF is exacerbated at high pH in cement with a too high content in
- AFt + OH– → AFm
The complete reaction can be derived from the molecular formulas of the reagents and products involved in the reaction. This reaction favors the dissolution of AFt and the formation of AFm. When combined, it is an aggravating factor of the harmful effect of too high temperatures. To minimize DEF, the use of low-alkali cements is also recommended. The detrimental crystallization of ettringite (AFt) preferentially occurs when concrete is exposed to water infiltrations and that the pH decreases due to the leaching of the (OH–) ions: the reaction is reversed as when temperature decreases.
External sulfate attacks (ESA)
Sulfates in solution in contact with concrete can cause chemical changes to the cement, which can cause significant microstructural effects leading to the weakening of the cement binder (chemical sulfate attack). Sulfate solutions can also cause damage to porous cementitious materials through crystallization and recrystallization (salt attack).
- H2S + 2 O2 → 2 H+ + SO2−4
or,
- HS− + 2 O2 → HSO−4
The corrosion often present in the crown (top) of concrete sewers is directly attributable to this process – known as crown rot corrosion.[7]
Thaumasite form of sulfate attack (TSA)
Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si(OH)6(CO3)(SO4)·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O.
TSA is sometimes easily recognizable on the field when examining the altered concrete. TSA-affected concrete becomes powdery and can be dug with a scoop, or even scrapped with the fingers. Concrete decohesion is very characteristic of TSA.
TSA was first identified during the years 1990 in
Full pyrite oxidation can be schematized as:
- 2 FeS2 + 7.5 O2 + 4 H2O → Fe2O3 + 4 H2SO4
The sulfuric acid released by pyrite oxidation then reacts with portlandite (Ca(OH
2)) present in the hardened cement paste to give gypsum:
- H2SO4 + Ca(OH)2 → CaSO4 · 2H2O
When concrete also contains limestone aggregates or a filler addition, H
2SO
4 reacts with calcite (CaCO
3) and water to also form gypsum while releasing CO2:
- H2SO4 + CaCO3 + H2O → CaSO4 · 2H2O + CO2
Gypsum is relatively soluble in water (~ 1 – 2 g/L), so there is plenty of calcium and sulfates ions available for TSA.
Simultaneously, carbonic acid (H2O + CO2 ⇌ H2CO3) dissolves calcite to form soluble calcium bicarbonate:
- H2O + CO2 + CaCO3 → Ca(HCO3)2
So, when all the chemical ingredients necessary to react with C-S-H from the hardened cement paste in concrete are present together the TSA reaction can occur. When grounds rich in pyrite, such as many clays or marls, are excavated for civil engineering works, the strong acidification produced by pyrite oxidation is the powerful driving force triggering TSA because it frees up and mobilizes all the ions needed to attack C-S-H and to form thaumasite (CaSiO3·CaCO3·CaSO4 · 15H2O).
TSA is favored by a low temperature, although it can be encountered at higher temperature in warm areas. The reason is to be found in the
Calcium leaching
When water flows through cracks present in concrete, water may dissolve various minerals present in the hardened cement paste or in the aggregates, if the solution is unsaturated with respect to them. Dissolved ions, such as calcium (Ca2+), are leached out and transported in solution some distance. If the physico-chemical conditions prevailing in the seeping water evolve with distance along the water path and water becomes supersaturated with respect to certain minerals, they can further precipitate, making calthemite deposits (predominately calcium carbonate) inside the cracks, or at the concrete outer surface. This process can cause the self-healing of fractures in particular conditions.
Fagerlund[9] (2000) determined that, “About 15% of the lime has to be dissolved before strength is affected. This corresponds to about 10% of the cement weight, or almost all of the initially formed Ca(OH)2.” Therefore, a large amount of "calcium hydroxide" (Ca(OH)2) must be leached from the concrete before structural integrity is affected. The other issue however is that leaching away Ca(OH)2 may allow the corrosion of reinforcing steel to affect structural integrity.
Decalcification
Within set concrete there remains some free "calcium hydroxide" (Ca(OH)2),[1] which can further dissociate to form Ca2+ and hydroxide (OH−) ions".[10] Any water which finds a seepage path through micro cracks and air voids present in concrete, will readily carry the (Ca(OH)2) and Ca2+ (depending on solution pH and chemical reaction at the time) to the underside of the structure where leachate solution contacts the atmosphere.[11] Carbon dioxide (CO2) from the atmosphere readily diffuses into the leachate and causes a chemical reaction, which precipitates (deposits) calcium carbonate (CaCO3) on the outside of the concrete structure. Consisting primarily of CaCO3 this secondary deposit derived from concrete is known as "calthemite"[11] and can mimic the shapes and forms of cave "speleothems", such as stalactites, stalagmites, flowstone etc.[12] Other trace elements such as iron from rusting reinforcing steel bars may be transported and deposited by the leachate at the same time as the CaCO3. This may colour the calthemites orange or red.[13][14]
The chemistry involving the leaching of calcium hydroxide from concrete can facilitate the growth of calthemites up to ≈200 times faster than cave speleothems due to the different chemical reactions involved.[15] The sight of calthemite is a visual sign that calcium is being leached from the concrete structure and the concrete is gradually degrading.[11][16]
In very old concrete where the calcium hydroxide has been leached from the leachate seepage path, the chemistry may revert to that similar to "speleothem" chemistry in limestone cave.[11][12] This is where carbon dioxide enriched rain or seepage water forms a weak carbonic acid, which leaches calcium carbonate (CaCO3) from within the concrete structure and carries it to the underside of the structure.[17] When it contacts the atmosphere, carbon dioxide degasses and calcium carbonate is precipitated to create calthemite deposits,[11] which mimic the shapes and forms of speleothems.[12] This degassing chemistry is not common in concrete structures as the leachate can often find new paths through the concrete to access free calcium hydroxide and this reverts the chemistry to that previously mentioned where CO2 is the reactant.[11]
Sea water attack
Concrete exposed to
Effects of bacterial activity
- H2SO4 + Ca(OH)2 → CaSO4 + 2 H2O
- H2SO4 + CaO·SiO2·n H2O → CaSO4 + H2SiO3 + n H2O
In each case the soft expansive and water-soluble corrosion product of gypsum (CaSO4) is formed. Gypsum is easily washed away in wastewater causing a loss of concrete aggregate and exposing fresh material to acid attack.
Concrete floors lying on ground that contains pyrite (iron(II) disulfide) are also at risk. As a preventive measure sewage may be pretreated to increase pH or oxidize or precipitate the sulfides in order to minimize the activity of sulfide-reducing bacteria.[citation needed]
As bacteria often prefer to adhere to the surfaces of solids than to remain into suspension in water (planktonic bacteria), the biofilms formed by sessile (i.e., fixed) bacteria are often the place where they are the most active. Biofilms made of multiple layers (like an onion) of dead and living bacteria protect the living ones from the harsh conditions often prevailing in water outside biofilm. Biofilms developing on the already exposed surface of metallic elements encased in concrete can also contribute to accelerate their corrosion (differential aeration and formation of anodic zones at the surface of the metal). Sulfides produced by the SRB bacteria can also induce stress corrosion cracking in steel and other metals.
Physical damages
Construction defects
Damages can occur during the casting and de-shuttering processes. For instance, the corners of beams can be damaged during the removal of shuttering because they are less effectively compacted by means of vibration (improved by using form-vibrators). Other physical damages can be caused by the use of steel shuttering without base plates. The steel shuttering pinches the top surface of a concrete slab due to the weight of the next slab being constructed.
Concrete slabs, block walls and pipelines are susceptible to cracking during ground settlement, seismic tremors or other sources of vibration, and also from expansion and contraction during adverse temperature changes.
Various types of concrete shrinkage
- Chemical shrinkage (self-desiccation)
The cement hydration process consumes water molecules. The sum of the volumes of the hydration products present in the hardened cement paste is smaller than the sum of the volumes of the reacting mineral phases present in the cement clinker. Therefore, the volume of the fresh and very young concrete undergoes a contraction due to the hydration reaction: it is what is called "chemical shrinkage" or "self-desiccation". It is not a problem as long as the very fresh concrete is still in a liquid, or a sufficiently plastic, state and can easily accommodate volume changes (contraction).
- Plastic shrinkage
Later in the setting phase, when the fresh concrete becomes more viscous and starts to harden, water loss due to unwanted evaporation can cause "plastic shrinkage". This occur when concrete is placed under hot conditions, e.g. in the summer and not sufficiently protected against evaporation. Cracks often develop above reinforcement bars because the contraction of concrete is locally restrained at this level and the still setting and weakly resistant concrete cannot freely shrink.
- Cracks due to a poor curing (loss of water at early age)
The curing of concrete when it continues to harden after its initial setting and progressively develops its mechanical strength is a critical phase to avoid unwanted cracks in concrete. Depending on the temperature (summer or winter conditions) and thus on the cement hydration kinetics controlling the setting and hardening rate of concrete, curing time can require a few days only (summer) or up to two weeks (winter). It is then capital to avoid losses of water by evaporation because water is still necessary for continuing the slow cement hydration. Water loss at this stage aggravates concrete shrinkage and can cause unacceptable cracks to develop in concrete. Cracks form in case of a too short, or too poor, curing when young concrete has not yet developed a sufficient early strength to withstand tensile stress caused by undesirable and premature drying. Cracks development occurs when early-age concrete is insufficiently protected against desiccation and too much water evaporates with heat because of unfavorable meteorological conditions: e.g, high temperature, direct solar insolation, dry air, low
- Drying shrinkage
After sufficient setting and hardening of concrete (after 28 days), the progressive loss of capillary water is also responsible for the "drying shrinkage". It is a continuous and long-term process occurring later during the concrete life when under dry conditions the larger pores of concrete are no longer completely saturated by water.
- Thermal cracks
When concrete is subject to an excessive temperature increase during its setting and hardening as in massive concrete structures from where cement hydration heat cannot easily escape (semi-
Restrained shrinkage
When a concrete structure is heavily reinforced, the very dense rebar network can block the contraction movement of the protecting
The formation of fissures in the concrete cover above the reinforcement bars represents a preferential pathway for the ingress of water and aggressive agents such as CO2 (lowering of pH around the rebar) and chloride anions (pitting corrosion) into concrete. The physical formation of cracks therefore favors the chemical degradation of concrete and aggravates steel corrosion. Physical and chemical degradation processes are intimately coupled, and the presence of water infiltrations also accelerates the formation of expansive products of harmful swelling chemical reactions (iron corrosion products, ASR, DEF, ISA, ESA).
Different approaches and methods have been developed to attempt to quantitatively estimate the influence of cracks in concrete structures on carbonation and chloride penetration.[19] Their aim is to avoid underestimating the penetration depth of these harmful chemical agents and to calculate a sufficient thickness for the concrete cover to protect the rebar against corrosion during the whole service life of the concrete structure.
Freeze-thaw cycles
In winter conditions, or in cold climates, when the temperature falls below 0 °Celsius, the
Mechanical damages
Overload, shocks and vibrations (bridges, roads submitted to intense truck traffic...) can induce
Thermal damages
Due to its low
Up to about 300 °C, the concrete undergoes normal thermal expansion. Above that temperature, shrinkage occurs due to water loss; however, the aggregate continues expanding, which causes internal stresses. Up to about 500 °C, the major structural changes are carbonatation and coarsening of pores. At 573 °C, quartz undergoes rapid expansion due to phase transition, and at 900 °C calcite starts shrinking due to decomposition. At 450-550 °C the cement hydrate decomposes, yielding calcium oxide. Calcium carbonate decomposes at about 600 °C. Rehydration of the calcium oxide on cooling of the structure causes expansion, which can cause damage to material which withstood fire without falling apart. Concrete in buildings that experienced a fire and were left standing for several years shows extensive degree of carbonatation from carbon dioxide which is reabsorbed.
Concrete exposed to up to 100 °C is normally considered as healthy. The parts of a concrete structure that is exposed to temperatures above approximately 300 °C (dependent of water/cement ratio) will most likely get a pink color. Over approximately 600 °C the concrete will turn light grey, and over approximately 1000 °C it turns yellow-brown.[21] One rule of thumb is to consider all pink colored concrete as damaged that should be removed.
Fire will expose the concrete to gases and liquids that can be harmful to the concrete, among other salts and acids that occur when gases produced by a fire come into contact with water.
If concrete is exposed to very high temperatures very rapidly, explosive spalling of the concrete can result. In a very hot, very quick fire the water inside the concrete will boil before it evaporates. The steam inside the concrete exerts expansive pressure and can initiate and forcibly expel a spall.[22]
Radiation damages
Exposure of concrete structures to
However,
Repairs and strengthening
It may be necessary to repair a concrete structure following damage (e.g. due to age, chemical attack, fire,[23] impact, movement or reinforcement corrosion). Strengthening may be necessary if the structure is weakened (e.g. due to design or construction errors, excessive loading, or because of a change of use).
Repair techniques
The first step should always be an investigation to determine the cause of the deterioration. The general principles of repair include arresting and preventing further degradation; treating exposed steel reinforcement; and filling fissures or holes caused by cracking or left after the loss of spalled or damaged concrete.
Various techniques are available for the repair, protection and rehabilitation of concrete structures,[24] and specifications for repair principals have been defined systematically.[25] The selection of the appropriate approach will depend on the cause of the initial damage (e.g. impact, excessive loading, movement, corrosion of the reinforcement, chemical attack, or fire) and whether the repair is to be fully load bearing or simply cosmetic.
Concrete stitching employs metal staples or stitches to restore structural integrity to cracked concrete surfaces. This method applies torque across the crack, effectively transferring load and tension to stabilize and strengthen the affected area. Recognized for its simplicity and minimal disruption, concrete stitching is widely utilized in essential infrastructures such as bridges and buildings, significantly prolonging the lifespan of concrete structures by preventing crack propagation.
Repair principles which do not improve the strength or performance of concrete beyond its original (undamaged) condition include replacement and restoration of concrete after spalling and delamination; strengthening to restore structural load-bearing capacity; and increasing resistance to physical or mechanical attack.
Repair principles for arresting and preventing further degradation include control of anodic areas; cathodic protection, cathodic control; increasing resistivity; preserving or restoring passivity; increasing resistance to chemical attack; protection against ingress of adverse agents; and moisture control.
Techniques for filling holes left by the removal of spalled or damaged concrete include mortar repairs; flowing concrete repairs and sprayed concrete repairs. The filling of cracks, fissures or voids in concrete for structural purposes (restoration of strength and load-bearing capability), or non-structural reasons (flexible repairs where further movement is expected, or alternately to resist water and gas permeation) typically involves the injection of low viscosity resins or grouts based on epoxy, PU or acrylic resins, or micronised cement slurries.[26]
One novel proposal for the repair of cracks is to use bacteria. BacillaFilla is a genetically engineered bacterium designed to repair damaged concrete, filling in the cracks, and making them whole again.
Strengthening techniques
Various techniques are available for strengthening concrete structures, to increase the load-carrying capacity or else to improve the in-service performance. These include increasing the concrete cross-section and adding material such as steel plate or fiber composites[27][28] to enhance the tensile capacity or increase the confinement of the concrete for improved compression capacity.
See also
- Calthemite
- Concrete fracture analysis
- Corrosion of rebar
- Electrical resistivity measurement of concrete
- Interfacial Transition Zone(ITZ)
- Pitting corrosion of rebar
- Reinforced concrete structures durability
References
- ^ )
- ^ Borrows, P. (2006). "Chemistry Outdoors. School Science Review". Outdoor Science. 87 (320). Hartfield, Herts, UK: Association of Science Education: 24–25.
- ^ Borrows, Peter (2006-11-01). "Concrete chemistry". Letters. Education in Chemistry. Vol. 43, no. 6. Royal Society of Chemistry. p. 154. Retrieved 2018-06-19.
- ^ "Accelerating Concrete Set Time". US Federal Highway Administration. 1999-06-01. Archived from the original on 2007-01-17. Retrieved 2007-01-16.
- .
- ISBN 978-0471958420.
- ISBN 0-07-054970-2.
- ISBN 978-0-7277-3909-4.
- ^ Fagerlund, G. (2000). "Leaching of concrete: the leaching process: extrapolation of deterioration: effect on the structural stability". Report TVBM. 3091. Division of Building Materials, LTH, Lund University.
- Taylor and Francis
- ^ ISSN 1356-191X.
- ^ a b c Hill, C. A.; Forti, P. (1997). Cave Minerals of the World (2 ed.). Huntsville, Alabama: National Speleological Society Inc. pp. 217, 225.
- ^ White, W. B. (1997). "Color of Speleothems". In Hill, C.; Forti, P. (eds.). Cave Minerals of the World (2 ed.). Huntsville, Alabama: National Speleological Society Inc. pp. 239–244.
- ^ "Water Damage Repair". Retrieved 2021-02-12.
- ^ Sefton, M. (1988), "Manmade speleothems", South African Speleological Association Bulletin, 28: 5–7
- S2CID 53626764.
- S2CID 129704545
- ^ Hydrogen Sulfide Corrosion in Wastewater Collection and Treatment Systems. Washington, DC, USA: U.S. Environmental Protection Agency. 1991. pp. 1–5, 6.
- . Retrieved 2022-01-19.
- ^ "ASTM E119".
- ^ Fire-damage to buildings, Norwegian Building Research Institute, publication 24
- ^ "Spalling and preventative measures". sustainableconcrete.org.uk. 2011-10-03. Archived from the original on 2011-10-03.
- ^ Assessment, design and repair of fire-damaged concrete structures, The Concrete Society, 2008
- ISBN 978-0-87031-933-4.)
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: CS1 maint: numeric names: authors list (link - ISBN 0-580-45057-0
- ISBN 978-1-78262-814-9
- ISBN 978-3-43303086-8
- ISBN 978-0-08100636-8.
Further reading
- Hirao, Hiroshi; Yamada, Kazuo; Takahashi, Haruka; Zibara, Hassan (2005). "Chloride binding of cement estimated by binding isotherms of hydrates". Journal of Advanced Concrete Technology. 3 (1): 77–84. ISSN 1346-8014. Retrieved 2022-02-19.
- Galan, Isabel; Glasser, Fredrik P. (2015-02-01). "Chloride in cement". Advances in Cement Research. 27 (2): 63–97. ISSN 0951-7197. Retrieved 2022-02-19.