Table 3.
Research and tests used to assess the pozzolanic activity of clays.
| Research | Methods Employed | Main Results | |
|---|---|---|---|
| 01 | [108] | Thermogravimetric analysis, calorimetry, mechanical strength and X-ray diffraction | Increased compressive strength verified by strength activity index test; observation in XRD diffraction characterization of a higher cement substitution factor and slow pozzolanic reaction, progress of pozzolanic reaction observed with thermal analysis. |
| 02 | [109] | Mechanical strength | Progression of compressive strength at all ages verified by strength activity index test. |
| 03 | [110] | Chapelle, thermogravimetric analyses, X-ray diffraction and X-ray fluorescence |
It was observed with the compressive strength that the materials compared to the clay show distinct performance; TGA pointed out total portlandite was consumed representing good pozzolanic reaction of the calcined clay. |
| 04 | [111] | Mechanical strength and X-ray diffraction | XRD was used to characterize the clay to form the metakaolin and mechanical strength to measure the progress of the compressive strength of the geopolymer. |
| 05 | [112] | Mechanical strength | Observation of the increase or similarity of the mechanical strength of concretes with calcined clay. |
| 06 | [113] | Mechanical strength | Good behavior of metakaolin with steel fibers and increased compressive strength, especially at older ages. |
| 07 | [42] | Chapelle, mechanical resistance and X-ray diffraction | XRD was used to characterize the clays, observing the complete dehydroxylation of kaolinite after calcination at 750 °C, pointing to pozzolanic reactivity through the chaplet method, confirmed by thermal analysis, and the compressive strengths of the mortars were equal or superior to the reference ones. |
| 08 | [114] | Frattini, mechanical resistance, X-ray diffraction and X-ray fluorescence | Mechanochemical activation potentiated the pozzolanic activity of natural clays, the strength activity index, and the Frattini test confirmed the increase in pozzolanic reactivity; XRD investigations pointed out the ability of clays to act as pozzolans. |
| 09 | [115] | Mechanical strength and X-ray diffraction | XDR pointed out the dehydroxylation of kaolinite at 600 °C and the strength activity index showed higher compressive strengths at later ages. |
| 10 | [116] | Calorimetry and X-ray diffraction | XRD was used for characterization and gauged the presence of kaolinite in the clays, isothermal calorimetry was used to rapidly probe the reactivity of kaolinite clays, and thermal analysis quantified the kaolinite showing a strict directly proportional link between the kaolinite content of the crude clay and reactivity of the calcined clay. |
| 11 | [19] | R3, X-ray diffraction and X-ray fluorescence | Calcined clays were characterized by XRD and XFR, pointing out the potentiality of the material and the pozzolanic R3 test showed that the clays are significantly more reactive than fly ash and comparable to slag and silica fume. |
| 12 | [117] | Frattini, Luxàn, X-ray diffraction, X-ray fluorescence, thermogravimetric analysis and mechanical strength | The XRD indicated the potentiality of the material in its characterization, the electrical conductivity confirmed that the natural pozzolans can be classified as of low reactivity, the Frattini test and the thermogravimetric analysis confirmed the pozzolanic behavior of the natural pozzolans being these results confirmed by mechanical tests with strength gain around 13 to 15% at advanced ages. |
| 13 | [118] | R3, X-ray diffraction and X-ray fluorescence | XRD was possible the mineralogical characterization of 13 different clay-rich raw materials pointing to an evaluation of the previous pozzolanic reactivity being confirmed by the R3 calorimetry test where kaolinite influences the heat of hydration. |
| 14 | [119] | Chapelle, R3, X-ray diffraction and mechanical strength | The XRD was a primary analysis to explain the difference in behavior between the materials; there was an increase in the strength of the mortars with calcined clay measured by compressive strength, the R3 test also showed pozzolanic reactivity of the clays. |
| 15 | [120] | Chapelle and X-ray diffraction | The XRF characterized and pointed out the pozzolanic activity of the material as well as the XRD revealed that the presence of the material in the system increases the presence of CSH. The Chapelle test confirmed that the increase in compressive strength was due to the pozzolanic reaction of the material. |
| 16 | [7] | Unusual comparative analysis, X-ray diffraction and X-ray fluorescence | The XRF and XRD characterized the material pointing pozzolanic potential. The pozzolanic reactivity was measured by unconventional tests. |
| 17 | [76] | Chapelle, thermogravimetric analysis, X-ray diffraction and X-ray fluorescence |
The XRF and XRD characterized the material, pointing to pozzolanic potential. The combination of X-ray diffraction (XRD) and thermogravimetric (TG) techniques differentiated the difference of calcining and grinding. The Chapelle test pointed out better pozzolanic reactivity of the material compared to the commercial one. |
| 18 | [105] | Mechanical strength | The mechanical strength was used to assess the pozzolanic development of the material in the cement matrix. |
| 19 | [121] | Mechanical resistance, calorimetry and X-ray fluorescence |
The XRD was used to measure the crystalline phases. The calorimetry showed the formation of hydrates pointing to a pozzolanic reaction with the formation of CSH. The compressive strength of the cementitious matrices showed a decrease when percentages higher than 30% were substituted as well as presenting the development of pozzolanic reactivity of the material. |
| 20 | [122] | Mechanical strength, Luxàn and X-ray fluorescence |
XRF was used for characterization of the materials. The Lùxan test indicated a medium pozzolanicity of the material that induces filling behavior in the cement matrix. The incorporation of the residue increased the mechanical strength. |
| 21 | [57] | Thermogravimetric analysis, calorimetry and X-ray diffraction |
The results of calorimetry, XRD and TG revealed the pozzolanic reaction of the calcined clay, and due to the pozzolanic reaction, there was a greater production of HSC increasing the mechanical strength. |
| 22 | [123] | Mechanical strength, unusual comparative analyses, X-ray diffraction and calorimetry | XRD and DTA/TG studies confirmed declines in portlandite content and CSH formation. Using less usual standardized tests, the cements were considered pozzolanic. Mechanical performance analysis reinforced the pozzolanic potentiality of the material. |
| 23 | [124] | Mechanical strength, unusual comparative analyses and thermogravimetric analysis | The aforementioned tests have shown that the red clay has a higher potential compared to the others. |
| 24 | [125] | Mechanical strength | The pozzolanic potential of the materials was tested by the mechanical behavior of mortars, showing a positive effect on the properties. It was observed that the pozzolanic materials can improve the environmental resistance of the mortar. |
| 25 | [126] | Frattini, Chapelle, mechanical strength, thermogravimetric analysis, calorimetry, X-ray diffraction and X-ray fluorescence |
The pozzolanic activity of the clays was evaluated by calcium hydroxide fixation (Chapelle), Frattini test and compressive strength, indicating that when calcined at 650 °C, they presented pozzolanic activity and a percentage increase in compressive strength. |
| 26 | [127] | Chapelle, mechanical strength | The results of the pozzolanic activity evaluation by the Chapelle method showed that this material has potential to be used as a pozzolan. In the mechanical strength analysis, the ternary mixtures with the material and limestone resulted in higher compressive strength. |
| 27 | [128] | Mechanical strength, thermogravimetric analysis, X-ray diffraction and X-ray fluorescence |
The thermal transformation of the materials was studied by TG-DTA and XRD, pointing out the temperatures of the transformations of each phase. The pozzolanicity was measured at 7 days and the strength activity index by mechanical resistance had a significant increase. The material, when calcined, presents itself as a reactive pozzolan but with later reactions. |
| 28 | [129] | Chapelle and mechanical strength | The Chapelle test and the resistance activity index were used to evaluate the pozzolanic activity of the material after thermal treatment, indicating higher pozzolanic activity when calcined. |
| 29 | [86] | Luxán | The evaluation of pozzolanicity was necessary to understand how the material behaves in the reactive process with the cement used in the matrix and showed good pozzolanic reactivity according to the Lùxan method, enabling improvements in technological properties such as mechanical strength. |
| 30 | [130] | Frattini, mechanical strength, X-ray diffraction and X-ray fluorescence | With the characterization tests, such as XRD, mechanical resistance analysis and pozzolanicity tests, it was possible to determine that the clays can replace cement in mortars. The incorporation of the material increased the density of the mortar; however, its mechanical resistance decreased. |
| 31 | [131] | Mechanical strength, unusual comparative analyses, X-ray diffraction and X-ray fluorescence | With the applied methodology, it was possible to observe that the partial replacement of cement in the mortars by clays resulted in considerable improvement in the compressive strength at 28 days. The pozzolanic reactivity of clays A and B is explained by the characterization of structural changes after calcination with XRD, thermal and unconventional analysis. |
| 32 | [99] | Mechanical resistance, thermogravimetric analysis and calorimetry | The resistance activity indexes meet the requirements for a pozzolanic material. The results of compressive strength indicated that the optimum strength to replace Portland cement up to 30% was viable for the use of the brick waste. |
| 33 | [132] | Frattini | With Frattini’s method it was possible to evaluate that the material in question ci exhibited greater pozzolanic activity than non-activated blended cement samples, even though it was considered non-pozzolanic. |
| 34 | [133] | Unusual comparative analysis and X-ray diffraction | During the work, the characterization of the material was carried out by XRD and unconventional methods to assess the development of pozzolanic reactivity. The calcium adsorption by kaolinite increased with the increase in the initial concentration of hydrated lime causing the pozzolanic reaction to be delayed in the long term. |
| 35 | [134] | Mechanical strength and X-ray diffraction | To assess the pozzolanic activity, XRD was used for material characterization and mechanical resynthesis to assess the pozzolanic development. The results showed a decline in the physical properties of the material as well as in the mechanical strength when larger size material is used. |
| 36 | [135] | Chapelle, thermogravimetric analysis and X-ray diffraction | The pozzolanic potentials were investigated using a novel method involving TGA/dTG and XRD techniques, in addition to the Chapelle method. The results provided insights for the development of restoration mortars. |
| 37 | [136] | Thermogravimetric analysis and X-ray diffraction | The mineralogical changes were monitored through X-ray diffraction (XRD) and thermogravimetric analysis. Different lime contents of the treated samples were used to assess the development of pozzolanic reactions. It was observed that the clays exhibited low reactivity, resulting in a delay in the precipitation of new hydrated phases. |
| 38 | [137] | Frattini, mechanical strength and Luxàn | The materials, 3 clays, were selected and characterized. After calcination at 700 °C and grinding, the pozzolanic activity was determined by means of the electrical conductivity test, Frattini test and compressive strength index. The results show that all calcined clays are classified as highly reactive pozzolanic. |
| 39 | [138] | Mechanical strength, thermogravimetric analysis, calorimetry, X-ray diffraction and X-ray fluorescence | Preliminary analyses such as XRD show a difference in its metakaolinite content. Isothermal calorimetry and compressive strength tests were performed, complementing the analysis of the development of pozzolanic reactivity in the matrix being monitored the hydration reaction by thermogravimetric analysis (TGA). As a main result, it was found that the reactivity of the materials are distinct. |
| 40 | [139] | Frattini, mechanical strength, calorimetry, X-ray diffraction and X-ray fluorescence | In this work, it was observed that the clay can be calcined to form a technically feasible supplementary cementitious material since the compressive strength of the concrete showed results similar to other materials already in use. The XRD characterization showed a reduction in crystallinity and increase in amorphous phases in samples calcined at 600 ºC confirmed by thermal analyses. The Frattini test indicates continuous pozzolanic reaction with curing time. |
| 41 | [140] | Mechanical strength | The incorporation and additions in the cement allowed for mortars to be obtained with higher physical-mechanical properties and durability than the reference mortar. However, mixtures containing glass powder and/or metakaolin showed higher strength than those containing brick waste. |
| 42 | [141] | Chapelle and X-ray diffraction | XRD was performed to characterize and quantify the amount of silica in the material. With the modified Chapelle test, it was possible to determine that the highest amounts of fixed lime were found at 700 and 800 °C, i.e., the highest pozzolanic reactivity at these temperatures. |
| 43 | [102] | Frattini and X-ray fluorescence | In conjunction with XRF and Frattini’s method it was observed that at higher temperatures a decrease in reactivity occurs. The reactivity of the clay increases directly proportional to the calcination temperature, with the limit at a temperature of 900 °C. |
| 44 | [69] | Chapelle, mechanical strength, R3 and calorimetry | Very good correlations were found between the compressive strength of the mortar and both measurements of chemical reactivity, presenting a new and fast method indicated especially for calcined clays, first being obtained by measuring the heat release during the reaction using isothermal calorimetry and second by determining the bound water. |
| 45 | [142] | Mechanical strength, thermogravimetric analysis and calorimetry | According to the mechanical strength, thermogravimetric analysis and calorimetry methods, the ideal heat treatment is 700 °C, the replacement rate of clinker for the material is 10% and the mortars containing the material have good mechanical strength. |
| 46 | [143] | Mechanical strength | The partial replacement of ordinary Portland cement by calcined clay in the mortars showed equal strength and decreased thermal conductivities. |
| 47 | [144] | Mechanical strength, thermogravimetric and calorimetric analysis and X-ray diffraction | Thermogravimetric, differential scanning calorimetry and X-ray diffraction analyses were performed to find out the evolution of the microstructure of the mortar with the material as well as analysis of its development with respect to compressive strength. With this, it can be concluded that the material improved the acid attack resistance in the mortars, increasing the CSH content, resulting in filler and pozzolanic activity. |
| 48 | [145] | Mechanical strength, thermogravimetric analysis and X-ray diffraction and X-ray fluorescence | In this work, the results obtained from the analysis of the material indicated its potential use in mortars when calcined at 750, 850, and 950 °C. For this, physical, chemical, mechanical and microstructural analyses were performed. The XRD revealed the dehydroxylation and transformation of kaolinite into metakaolin, confirmed by thermal analysis. The mechanical performance of all mortars increases steadily with age. |
| 49 | [4] | Mechanical strength, thermogravimetric analysis and calorimetry and X-ray diffraction and X-ray fluorescence | Reactive pozzolans can be obtained from low-grade kaolinitic clays, if properly calcined. The material was characterized by XRD, XRF and TGA-DTA. The pozzolanic reactivity was evaluated by compressive strength in mortars. The evolution of pozzolanic reactivity is limited at temperatures between 800 and 900 °C. The results point out that clays with moderate kaolinite contents constitute a potential source of high reactivity for pozzolanic materials. |
| 50 | [146] | Chapelle, thermogravimetric analysis and X-ray diffraction | The calcined materials at temperatures of 600–900 °C were investigated by XRD and TGA techniques and the Chapelle test. The presence of alumina and its subsequent dehydroxylation in the calcination process was observed and confirmed by thermal analysis. The Chapelle test indicates a better pozzolanic reactivity at 800 º C where the density of the hydrates increased. The calcination of the material is strictly connected with its microstructure and pozzolanic activity. |
| 51 | [147] | Frattini and mechanical strength | The pozzolanic activity of the material was gauged by the Frattini test in conjunction with the compressive strength. The results show that the replacement in a percentage of 30% presents an improvement in the mechanical behavior. |
| 52 | [148] | Unusual comparative analysis, thermogravimetric Analysis, X-ray Diffraction and X-ray Fluorescence | The investigation of the materials was carried out at temperatures of 600–850 °C for the production of metakaolin with pozzolanic activity with the DTA/TG and XRD methods in order to specify the mineralogical composition and the extent of dehydroxylation. The pozzolanic activity was evaluated in order to gauge the optimum calcination temperature, obtained at 700 °C and 800 °C. The pozzolanic activity content for the materials was distinct at about 20%. |
| 53 | [149] | Chapelle, mechanical strength, thermogravimetric analysis and X-ray diffraction | Analyzing the results, it was possible to observe that the optimum condition for calcination to be 800 °C, presenting total dihydroxylation and greater pozzolanic reactivity. The research points out a percentage of 15% for ideal content of metakaolin produced based on the compressive strength since the mechanical properties were superior. |
| 54 | [150] | Chapelle, mechanical strength, thermogravimetric analysis and X-ray diffraction | In this work, the Chapelle test was used as screening to assess the potential materials to be used in mortars. The mechanical strength of the cementitious matrices was improved when compared to the use of other materials in OPC incorporation. |
| 55 | [151] | Mechanical strength and X-ray diffraction | In this work, the characterization of the material was carried out, and despite being crystalline, it presented pozzolanic activity and this can be verified by the methods of analysis in the work. Furthermore, the compressive strength of mortars was improved by the calcination process at high temperatures. |
| 56 | [152] | Frattini and mechanical strength | The results present both calcined kaolinitic clays as pozzolanic and effective with different reaction rates that is directly related to their specific surface area in the post-calcination process besides their crystalline structure. The material presents a very high-pozzolanic activity allowing high levels of substitution. |
| 57 | [153] | Mechanical strength, thermogravimetric analysis, calorimetry, X-ray diffraction and X-ray fluorescence | The investigation provided the increase in reactivity of calcined clays by different factors. With the thermal treatment and with the analysis methods, an increase in the pozzolanic reactivity of the SCM was observed, which resulted in higher compressive strengths. |
| 58 | [154] | Mechanical strength, Luxán, thermogravimetric analysis and X-ray diffraction | The experimental results indicated that the calcined material has a higher strength performance if compared to its natural state and this is due to the increased pozzolanic reactivity as well as the decreased porosity and refined pore structure of the hardened cementitious system. |
| 59 | [155] | Mechanical strength and X-ray diffraction | This work assessed the technical feasibility of introducing up to 20% by weight of red mud in mortars. The gain in compressive strength was not attributed to the pozzolanic reaction because in its characterization, the material showed no evidence of pozzolanic reaction. |
| 60 | [156] | Frattini, mechanical strength, thermogravimetric analysis and X-ray diffraction | The five clays were characterized by XRD, ATG and DTA chemical analysis and pointed out pozzolanic reactivity of the materials. However, the pozzolanic activity of the clays depends on the kaolinite content and their crystalline structure in which clays containing more than 50% kaolinite produce more reactive material. In the results, it is possible to observe the presence of alginate pozzolanic reactivity evaluated by the Frattini test and increased compressive strength. |