An Approach to Accurately Identifying Binders in Historic Mortars by the Combination of Microscopic and Microanalytical Techniques
Abstract
:1. Introduction
2. Materials and Methods
2.1. Samples and Analytical Background
2.2. SEM-EDS and Principal Component Analysis
2.3. Optical Microscopy—Petrography
3. Results and Discussion
3.1. SEM—EDS and Principal Component Analysis
3.2. Optical Microscopy—Petrography
4. Conclusions
- The interval ranges for the chemical compositions of the binders were obtained with precision through EDS analyses. The following interval of elemental ratios Al/Ca and Si/Ca were established for the types of binders identified in Table 5, ensuring the accuracy of the results.
Al/Ca | Si/Ca | |||
---|---|---|---|---|
Binder Type | Min. | Max. | Min. | Max. |
Air lime | 0.02 | 0.09 | 0.09 | 0.20 |
Natural hydraulic lime | 0.12 | 0.15 | 0.21 | 0.28 |
Natural cement | 0.12 | 0.16 | 0.23 | 0.35 |
Blended air lime and Portland cement (including ordinary, white, and Portland composite cement types) | 0.04 | 0.13 | 0.21 | 0.37 |
Portland cement (including ordinary and white types) | 0.03 | 0.23 | 0.21 | 0.45 |
Portland composite cements | 0.17 | 0.23 | 0.41 | 0.49 |
- PCA analysis did not significantly refine the clusters because the samples have similar representations of the principal components. This suggests that PCA should not be applied to samples with elements that exhibit the same weight in their chemical composition.
- When dealing with overlapping grouped chemical results, optical microscopy is a critical step in identifying the key compounds of the binder. When consistently applied by a skilled petrographer, this practice ensures the accuracy and reliability of the results.
- Of the key compounds mentioned above, some stand out in helping to distinguish between historical hydraulic binders, such as: natural cement binders (calcined marl fragments, under-burned, well-burned, and over-burned marl fragments, presence of unhydrated C2S crystals and the absence (or minimal presence) of alite); NHL binders (presence of small dark inclusions (non-hydrated relicts of C2S), hydration rims around individual hydraulic phases, presence of gehlenite); and portland cement binders (large size of the unhydrated C3S crystals in historic Portland cement and ubiquity of C3S in all types of Portland cement).
- In blended mortars, the pastes’ homogeneity, or compositional variability, which may be attributable to the influence of the raw materials’ composition, varying according to their provenance, points to being influential in EDS analyses.
- Although some of the samples analyzed were manufactured in the laboratory, namely the natural hydraulic lime, Portland cement, and air lime mixed with Portland cement test specimens, the chemical results can be extrapolated to these types of binders, historically applied in other periods, since the raw materials and calcination temperatures are similar to those obtained in the past, even though today there is greater quality control in the manufacturing processes.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Sample ID | Construction Period | Case Study/Building | Type of Building | Binder Type | Binder to Aggregate Ratio by Weight (b:a) |
---|---|---|---|---|---|
CVT1B | 1902–1903 | CVT (1903)/ Ventura Terra building (Lisbon) | Residencial | AL | 1:5.4 |
CVT1C | AL | 1:7.8 | |||
CVT3B | AL | 1:4.3 | |||
AR49-2B | 1920–1923 | AR49 (1923)/ Luiz Rau building (Lisbon) | Residential | AL | (c) |
AR49-6C | AL | 1:5.8 | |||
AR49-7B | AL | 1:3 | |||
AR49-8A | AL | 1:2.9 | |||
AR49-8B | AL | 1:11.2 | |||
AR49-11B | AL | 1:6.7 | |||
AR49-15B | AL | 1:7.1 | |||
AR49-15C | AL | 1:7.9 | |||
IRF1B | 1934–1938 | IRF (1938)/Nossa Senhora de Fátima church (Lisbon) | Church | AL+OPC | 1:0.1:7 |
IRF2A | AL | 1:4.3 | |||
IRF2B | AL | 1:9.9 | |||
IRF3A | AL | 1:4.2 | |||
IRF3B | AL | 1:8 | |||
IRF4A | AL+OPC | 1:0.4:5.4 | |||
IRF7A | AL+OPC | 1:0.4:3.8 | |||
IRF7B | AL+OPC | 1:0.4:5.3 | |||
CBP1A | 1938–1939 | CBP (1939)/Bernardo da Maia house (Lisbon) | Residential | AL | 1:8.4 |
CBP4B (d) | OPC | 1:20.3 | |||
CBP6B | AL | 1:8.7 | |||
CBP7B | AL | 1:11.2 | |||
DN9A | 1936–1940 | DN (1940)/Diário de Notícias building (Lisbon) | Office and service | OPC | 1:6.1 |
DN10A | OPC | 1:7 | |||
DN11A | OPC | 1:7.4 | |||
DN11B | OPC | 1:4.2 | |||
DN12A | OPC | 1:12.9 | |||
DN12B | AL+OPC | 1:2.1:15.1 | |||
DN12C | OPC | 1:4.2 | |||
DN12D | AL | 1:4.3 | |||
DN19B | PCC | 1:25.2 (a) | |||
DN19C | OPC | 1:8.9 | |||
DN19D | AL+PCC | 1:1:6 (a) | |||
AAC1A | 1942–1944 | AAC (1944)/Cristino da Silva building (Lisbon) | Residential | AL+OPC | 1:0.2:6.1 |
AAC1B | AL+OPC | 1:0.2:7 | |||
AAC2A (c) | AL+WPC | 1:0.3:1.0 | |||
AAC2B | OPC | 1:24.5 | |||
AAC3A (c) | OPC | 1:3.0 | |||
AAC4A (c) | OPC | 1:1.9 | |||
LIP1A | 1955–1957 | LIP (1954)/Laboratories of Pasteur Institute of Lisbon (Lisbon) | Laboratory and services | OPC | 1:7.6 |
LIP9A | OPC | 1:6.6 | |||
EUA53-2A (c) | 1966–1969 | EUA53 (1970)/America building (Lisbon) | Residential and commercial | WPC (e) | 1:3.7 |
EUA53-2B | OPC | 1:6.7 | |||
EUA53-3A (c) | WPC (e) | 1:19.1 | |||
EUA53-3B | OPC | 1:4.9 | |||
EUA53-4A (c) | WPC | 1:11.1 | |||
EUA53-4B | OPC | 1:11.5 | |||
FCG4A | 1963–1969 | FCG (1975)/Calouste Gulbenkian Foundation Headquarters and Museum (Lisbon) | Office and cultural facilities | OPC | 1:10.2 |
JRP2A | 1984–1987 | JRP (1987)/Jacob Rodrigues Pereira Institute (Lisbon) | Educational/academic | PCC | 1:4.9 (a) |
UNL3A | 2000–2002 | UNL (2002)/New University of Lisbon Rectory (Lisbon) | Educational/academic | OPC | 1:10.2 |
0-NC | 1887 | Hivernacle (Barcelona) | Greenhouse | NC | (b) |
1-NC | 1900 | Villarroel (Barcelona) | Residential | NC | (b) |
Specimens ID | Mortar Formulation | Binder Type | b:a (a) |
---|---|---|---|
CA-Sb-CP-360d | CL90-S air lime mortar with siliceous sand, 360 days laboratory curing | AL | 1:11 |
CA-AL-CP-360d | CL90-S air lime mortar with washed siliceous sand, 360 days laboratory curing | AL | 1:11 |
CH-AL-CP-360d | NHL 3.5 (1) mortar with washed siliceous sand, 360 days laboratory curing | NHL | 1:5.6 |
CH-Sb-CP-360d | NHL 3.5 (1) mortar with siliceous sand, 360 days laboratory curing | NHL | 1:5.6 |
CEM I (42.5) | Portland cement mortar (CEM I 42.5) with siliceous sand, 180 days laboratory curing | OPC | 1:3 |
CEM I (52.5) | Portland cement type mortar (CEM I 52.5) with siliceous sand, 180 days laboratory curing | OPC | 1:3 |
Li310-Ref-fib | Blended mortar with air lime and Portland cement (CEM I 42.5) with siliceous sand and organic fibers, 360 days laboratory curing | AL+OPC | 1:2.6:26.3 |
Li310-Ref | Blended mortar with air lime and Portland cement (CEM I 42.5) with siliceous sand, 360 days laboratory curing | AL+OPC | 1:2.6:26.3 |
CA-AL-CP-720d | CL90-S air lime mortar with washed siliceous sand, 720 days laboratory curing | AL | 1:11 |
CH-AL-CP-720d | NHL 3.5 (1) mortar with washed siliceous sand, 720 days laboratory curing | NHL | 1:5.6 |
124A | Blended mortars with air lime and white Portland cement (CEM I 42.5) with siliceous sand, 4 years laboratory curing | AL+WPC | 1:1.3:19.7 |
134A | AL+WPC | 1:0.9:17.5 |
Sample ID | Case Study | Binder Type | Al/Ca | Si/Ca | |
---|---|---|---|---|---|
CVT1B | Lisbon buildings | CVT (1903) | AL | 0.03 | 0.11 |
CVT1C | AL | 0.06 | 0.19 | ||
CVT3B | AL | 0.02 | 0.15 | ||
AR49-2B | AR49 (1923) | AL | 0.05 | 0.13 | |
AR49-6C | AL | 0.05 | 0.12 | ||
AR49-7B | AL | 0.02 | 0.10 | ||
AR49-8A | AL | 0.03 | 0.11 | ||
AR49-8B | AL | 0.05 | 0.19 | ||
AR49-11B | AL | 0.07 | 0.16 | ||
AR49-15B | AL | 0.05 | 0.14 | ||
AR49-15C | AL | 0.05 | 0.17 | ||
IRF1B | IRF (1938) | AL+OPC | 0.12 | 0.28 | |
IRF2A | AL | 0.04 | 0.09 | ||
IRF2B | AL | 0.04 | 0.12 | ||
IRF3A | AL | 0.06 | 0.12 | ||
IRF3B | AL | 0.05 | 0.14 | ||
IRF4A | AL+OPC | 0.11 | 0.35 | ||
IRF7A | AL+OPC | 0.13 | 0.32 | ||
IRF7B | AL+OPC | 0.11 | 0.30 | ||
CBP1A | CBP (1939) | AL | 0.07 | 0.20 | |
CBP4B | OPC | 0.23 | 0.44 | ||
CBP6B | AL | 0.03 | 0.13 | ||
CBP7B | AL | 0.09 | 0.21 | ||
DN9A | DN (1940) | OPC | 0.11 | 0.39 | |
DN10A | OPC | 0.09 | 0.34 | ||
DN11A | OPC | 0.10 | 0.40 | ||
DN11B | OPC | 0.10 | 0.33 | ||
DN12A | OPC | 0.12 | 0.44 | ||
DN12B | AL+OPC | 0.13 | 0.32 | ||
DN12C | OPC | 0.12 | 0.45 | ||
DN12D | AL | 0.05 | 0.15 | ||
DN19B | PCC | 0.23 | 0.41 | ||
DN19C | OPC | 0.07 | 0.31 | ||
DN19D | AL+PCC | 0.13 | 0.37 | ||
AAC1A | AAC (1944) | AL+OPC | 0.05 | 0.24 | |
AAC1B | AL+OPC | 0.09 | 0.27 | ||
AAC2A | AL+WPC | 0.05 | 0.22 | ||
AAC2B | OPC | 0.09 | 0.36 | ||
AAC3A | OPC | 0.10 | 0.31 | ||
AAC4A | OPC | 0.09 | 0.34 | ||
LIP1A | LIP (1954) | OPC | 0.13 | 0.35 | |
LIP9A | OPC | 0.07 | 0.32 | ||
EUA53-2A | EUA53 (1970) | WPC | 0.05 | 0.22 | |
EUA53-2B | OPC | 0.09 | 0.30 | ||
EUA53-3A | WPC | 0.03 | 0.21 | ||
EUA53-3B | OPC | 0.08 | 0.32 | ||
EUA53-4A | WPC | 0.08 | 0.30 | ||
EUA53-4B | OPC | 0.09 | 0.32 | ||
FCG4A | FCG (1975) | OPC | 0.11 | 0.33 | |
JRP2A | JRP (1987) | PCC | 0.17 | 0.49 | |
UNL3A | UNL (2002) | OPC | 0.08 | 0.27 | |
CA-Sb-CP-360d | Laboratory formulated test specimens | AL | 0.06 | 0.11 | |
CA-AL-CP-360d | AL | 0.05 | 0.07 | ||
CH-AL-CP-360d | NHL | 0.15 | 0.26 | ||
CH-Sb-CP-360d | NHL | 0.12 | 0.21 | ||
CEM I (42.5) | OPC | 0.09 | 0.33 | ||
CEM I (52.5) | OPC | 0.08 | 0.45 | ||
Li310-Ref-fib | AL+OPC | 0.05 | 0.25 | ||
Li310-Ref | AL+OPC | 0.05 | 0.27 | ||
CA-AL-CP-720d | AL | 0.06 | 0.17 | ||
CH-AL-CP-720d | NHL | 0.12 | 0.28 | ||
124A | AL+WPC | 0.04 | 0.21 | ||
134A | AL+WPC | 0.08 | 0.27 | ||
0-NC | Barcelona buildings | NC | 0.12 | 0.23 | |
1-NC | NC | 0.16 | 0.35 |
Authors [by Reference] | |||||||
---|---|---|---|---|---|---|---|
NHL and other hydraulic lime mortars/binders | [17] | [27] | [47] | [48] | [49,50] | [40,49,51] | [51] |
Large C2S and C3S phases in a small amount of a brown matrix consisting of C3A and C4AF. | Small clusters of C2S may be detected in trace quantities in hydraulic limes. | Dominant C2S grains can present striations in different directions | Presence of “hot spots” as part of the hydraulic phases that result from local higher temperatures in the lime kiln. | If reaction rims did not develop, hydraulic phases dispersed in the binder can nevertheless still be observed both as veins and as pore filling. | Presence of small dark inclusions (non-hydrated relicts of C2S) that can be easily recognised. | C3S can be formed due to an overheating of the raw materials during the production of NHL | |
C3S can also be present in smaller quantities. | Hydration rims can be observed around individual hydraulic phases as a colourless rim. | The presence of gehlenite is a valuable indicator of the distinction between cement and natural hydraulic lime. | C2S: dark brown crystals medium-high relief, shaded contours, and sub idiomorphic habit. | ||||
Natural cement | [16] | [23] | [27] | [13] | [52] | ||
The NC residual nodules exhibit strong zoning which is best visible in transmitted light with parallel polars. | Presence of lumps of calcined marls in the natural cement (due to the calcination and to the deficient milling technology). | Under polarised light, the matrix of natural cements often appears spotted with dark isotropic areas broken by bright but dense carbonated regions. | High proportion of non-reactive ‘nodules’ or relicts (under-burned, well burned, and over-burned). | Under-burned, well burned, and over-burned marl fragments. | |||
NC mortars can be identified equally well at low magnifications as their binders contain residual compounds that are larger than the clinker of historic Portland cement. | Presence of unhydrated C2S crystals. | The dispersed quartz grains and other sand-sized silicate minerals also aid in distinguishing natural cements. These tend to retain most of their original texture when burned at calcining temperatures. | The largest ‘nodules’ are of millimetre size. | NHL does not show calcined marl fragments and have a more homogeneous structure. | |||
Absence of unhydrated C3S crystals. | Contain greater percentage of relicts than either the hydraulic limes or the Portland cements. | Lime nodules can be observed in the NHL samples, while the natural cements lack these nodules. | |||||
OPC | [23] | [27] | [53,54,55] | ||||
Large size of the unhydrated C3S crystals in historic Portland cements. The calcination process in vertical kilns was longer than in a modern horizontal kiln and it allowed the C2S and C3S crystals to acquire a larger size than in modern Portland cement. | Portland cement pastes are homogeneously isotropic or dark-colored where cementitious gels have formed, broken only by thin dispersed grains of calcium hydroxide that appear bright-colored. | The unhydrated cement grains are identified by the optical properties of the cement minerals, primarily C3S and C2S. | |||||
WPC | [27] | ||||||
The C2S phases are not surrounded by a brown-colored crystallographically indistinct ferrite phase (absence of brownish C4AF in the residual cement grains). | |||||||
PCC | [53,54] | ||||||
Unhydrated fly ash particles; GBFS—glassy slag particles with reddish hydration rims. |
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Almeida, L.; Santos Silva, A.; Veiga, R.; Mirão, J. An Approach to Accurately Identifying Binders in Historic Mortars by the Combination of Microscopic and Microanalytical Techniques. Minerals 2024, 14, 844. https://doi.org/10.3390/min14080844
Almeida L, Santos Silva A, Veiga R, Mirão J. An Approach to Accurately Identifying Binders in Historic Mortars by the Combination of Microscopic and Microanalytical Techniques. Minerals. 2024; 14(8):844. https://doi.org/10.3390/min14080844
Chicago/Turabian StyleAlmeida, Luís, António Santos Silva, Rosário Veiga, and José Mirão. 2024. "An Approach to Accurately Identifying Binders in Historic Mortars by the Combination of Microscopic and Microanalytical Techniques" Minerals 14, no. 8: 844. https://doi.org/10.3390/min14080844