The occurrence of faults in the form of cracks in houses has become increasingly common, especially in
rural Sikkim. In some cases, the cracks are so huge that ordinary people are compelled to abandon their
homes and relocate. Such exceptional cases are observed in and around the region where dam and tunnel
construction has been undertaken.
A typical example of such cases is reported from the Dikchu-Singtam area. I had the fortune of meeting
an uncle from Tumin, where I asked him about his newly built house. The uncle replied, "Nani, ghar
futeyra kei chaina nee, ailey samma kamako paisa sappai haleyra banako ghar" (Son, the occurrence of cracks around the house is rampant, the money earned so far has been invested in building the house.).
His words were simple, but I quenched my heart as a Civil Engineering aspirant, compelling me to write
and aware my Sikkimese people regarding crack's occurrence and their possible remedies.
Occurrence:
Cracks typically result from loading in flawed areas within structural components. They begin as micro
fissures and, under further loading, expand and spread throughout the entire structure. Cracks in houses usually stem from faults in various structural elements, whether in the substructure or superstructure. The substructure, constructed below ground level, includes foundation components that transfer the overall load to the ground. Issues arise when the imposed load exceeds the soil's bearing strength or due to independent ground movements, such as fluctuations in groundwater levels or soil settlement differentials. Differential settlement occurs when one part of the foundation settles more than another, influenced by factors like soil type, moisture content, foundation shape, and soil weight. Such settlements are common in areas previously covered with trees, as their roots initially bear loads, and their decay in the later years can lead to differential settlement. Constructing houses in such areas is discouraged; however, properly removing such elements from the soil that cause the deterioration of the structure will also work. Also, growing vegetation around the house, especially plants with deep roots that affect the structure's foundation, is highly discouraged. Further, the foundation of the house is encouraged in the areas where the water level is negligible or bare minimum. The response of the differential settlement is visible in the superstructure as cracks, especially in brickworks. A superstructure is a structure that is built above the ground. Such a structure adds beams, columns, slabs, brickwork, etc, as elements to its list. Various loads, such as dead load (self-weight), wind load (wind pressure), seismic load (earthquake-generated force), shear load (sliding force), and live loads (time- dependent loads), contribute to the formation of cracks. Superstructure cracks are divided into a) Structural cracks, b) Non-structural cracks, and c) Cracks based on their width dimensions. Structural cracks result from design errors, construction defects, or overloading of components. Examples include extensive cracks in RCC beams and the buckling of columns. Non-structural cracks, conversely, are mainly due to internally induced stresses and do not compromise the structure's safety. These cracks can appear vertically, horizontally, or diagonally along walls or structural elements. While they may not jeopardize safety, they often detract from the building's aesthetics, creating an impression of instability.
Cracks based on width are classified as—thin cracks (less than 1mm), medium cracks (1-2mm), wide
cracks (more than 2mm), and crazing, which involves closely spaced fine cracks on surfaces, commonly
observed in floors or slabs. Besides being unsightly, cracks may increase maintenance costs, and in some cases, moisture penetration through cracks can exacerbate long-term structural damage. Understanding the types and causes of cracks is essential for effective diagnosis and appropriate remediation.
Remedies: For better understanding, the remedies are divided into two parts: remedies during
construction to ensure crack-free structure and remedies to cure visible cracks.
During Construction: Several factors require careful attention during house construction, including
material selection, cement mortar specifications, building design, and construction techniques. Using
high-quality materials such as bricks, aggregates, and cement is crucial. While visiting Sikkim, I was
frequently asked simple questions by locals, such as an uncle from Samdong, who queried, "Bhai,
Ambuja, Star, ra Dalmia cement ma k farak cha?" ("Brother, what is the difference between Ambuja, Star, and Dalmia Cement?") I replied that they are essentially the same. However, he persisted, asking, & quot;Tyso bhaeh Ambuja kina mangoo ani Star kina sasto?" ("Then why is Ambuja cement more expensive than Star cement?") This question, relevant to many in Sikkim, prompts consideration. I want to clarify that although the materials are similar, pricing varies due to brand value. Any brand of cement will offer similar strength after construction. Nonetheless, it's advisable to purchase cement close to its manufacturing date as strength degrades over time due to factors like moisture and transportation. Proper selection of aggregates is also crucial. Angular coarse aggregates are recommended for constructing beams, columns, and slabs, while fine aggregates (sand) should be free from dust and dirt. Adequate reinforcement with steel bars is also essential to meet strength criteria. Regarding cement mortar specifications, some believe adding extra cement enhances strength, but this isn't true due to cement composition, which includes lime, leading to shrinkage and microcrack formation when water is added.
Optimal cement content is advised. Proper centering work is critical to prevent cement water leakage,
which could compromise strength compliance. Additionally, using the correct amount of water is crucial;
excessive water lowers concrete strength. Curing is another vital task often neglected, especially during winter. Complete curing for 28 days is recommended, as 90% of concrete strength is achieved within this period, with the remaining 10% gradually attained through ongoing hydration. Ensuring compliance with probable design loads like seismic, dead, and live loads is also essential during construction. These consideration of the specifications mentioned are vital for constructing crack-free structures.
Remedies to ensure visible cracks: If the structure has already been built and the owner notices visible cracks, it's essential to diagnose the type of crack before implementing any remedial measures. Cracks can develop in two forms: active and dormant. Active cracks continue to lengthen over time, while dormant cracks remain stable. Here are some remedial measures that can be applied to address the cracks.
a) Drilling and Plugging: This method is typically employed when cracks are linear and accessible
at one end, commonly used for vertical cracks in retaining walls (known as "plum walls" in
Nepali). A hole is drilled near the crack and filled with grout as part of the repair process.
Horizontal cracks on such walls typically pose no structural threat since the line of compressive
loading is perpendicular to the crack length. Therefore, in such cases, crack treatment is
unnecessary.
b) Routing and Sealing: In this method, the cracks are widened (routed) and then filled with a
flexible sealant (sealing). This technique is commonly utilized to address cracks, particularly on
vertical and curved surfaces.
c) Epoxy Injection: Epoxy injection effectively bonds or welds cracks together, even as narrow as
0.002 inches, restoring the concrete's integrity, including its strength and stiffness. This method
involves applying a surface cap of non-sag epoxy to contain the crack and installing injection
ports into drilled holes at close intervals along horizontal, vertical, or overhead cracks.
d) Stitching: This method is employed for cracked wall reinforcement and masonry repairs, serving
as a permanent solution. It involves drilling holes on both sides of the cracks, followed by
cleaning the holes and anchoring the legs of the staples into the holes using a non-shrink grout.
e) Dry packing: This method involves placing low water content mortar into the cracks, followed by
tamping and ramping the mortar to ensure excellent contact between the existing concrete and the
mortar.
Although these basic remedial measures are often effective, there are situations where repairs may not
suffice, depending on the nature of the cracks. With advancing technology, newer methods are
continually being developed through extensive research and application. In the worst-case scenario, it's
advisable to consult with professionals to identify the root cause of the cracks and determine the best
solutions.
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