Notes on Mortar (Le mortier)

Présentation

• Présentée par Dr A. BELAIDI

• Technologie des matériaux de construction 1 (TMC 1)

• Université Aboubakr Belkaïd, Tlemcen, Faculté de Technologie, Département d’Architecture

Chapitre 7: Mortar (Le mortier)

1. Definition

• Mortar (Mortier): A building material composed of a binder (lime or cement), sand, water, and potentially additives.

  • Composition Variability: Mortar compositions can vary based on:

  • Type and dosage of binder

  • Admixtures and additions

  • Water content

  • Binders: Wide selection of cement and lime types, chosen based on:

  • Structure requirements

  • Environmental conditions

2. Composition and Manufacturing of Mortars

• Standard Components: Mortar can consist of various standard materials:

  • Standardized cements

  • Special cements (e.g., calcium aluminate, prompt cement)

  • Masonry binders

  • Lime

a. Binders

• Lime: Traditional mortar component, characterized by:

  • Excellent plasticity and water retention

  • Low mechanical strength and slow curing

  • Curing Process: Gradual carbonation from CO2 in the air, slowed in cold/humid environments.

• Masonry Binder: Commercial product that includes:

  • Portland cement

  • Inert mineral filler (limestone)

  • Admixtures (e.g., water-repellent agents, air-entraining agents)

  • Admixtures Definition: Chemical products modifying concrete and mortar properties, added in small amounts (~5% of cement weight).

b. Admixtures

• General Role: Modify physical properties of mortar and concrete.

c. Aggregates

• Sand: Most commonly used aggregate, serving to:

  • Increase compactness

  • Particle Size Range: 0.080 mm to 4 mm.

• Water: Plays a dual role in mortar by:

  • Hydrating the cement

  • Enhancing workability

  • Optimal Water Content: Should contain the maximum water compatible with workability.

3. The Different Types of Mortars

3.1. Cement Mortars

• Characteristics:

  • Very strong

  • Quick setting and hardening

• Typical Ratios:

  • Cement to sand: 1:3

  • Water-to-cement ratio: 0.35

  • Typical dosages: 300-400 kg cement per 1 m³ sand.

3.2. Lime Mortars

• Comparison: Less resistant than cement mortars, provide:

  • Smoother and more workable character

  • Slower hardening time

3.3. Mixed (Bastard) Mortars

• Composition: Binder as a mixture of cement and lime, typically in equal proportions but adjustable depending on application.

3.4. Mortars Produced On-Site

• Production Method:

  • Use of locally available cement (ordinary or special).

  • Sand is often natural (rounded) or crushed.

  • Mixing by hand or small concrete mixer.

3.5. Industrial Mortar

• Description: Manufactured with precision, using dry components packaged in bags for consistent quality. Requires only water addition before use.

4. Properties of Mortar

4.1. Fresh State

4.1.1 Workability

• Measurement Methods: Various devices, notably:

  • Shaking Table: The mortar is placed in a cone and subjected to shocks.

  • Measurement of Spread:

  • Spread percentage calculated using: $E($

    • Where:

    • $D_f$ = final diameter

    • $D_i$ = initial diameter

• Spread Results Table:

  • Very stiff: 10-30%

  • Stiff: 30-60%

  • Normal: 60-80%

  • Soft (very plastic): 80-100%

  • Very soft to fluid: >100%

4.2. Hardened State

• Preparation of Specimens:

  • Specimens measuring 4 × 4 × 16 cm cured in water at 20 °C, produced using standardized molds.

• Compaction Method: Applying 60 jolts from 15 mm height at frequency of 1 drop/sec for 60 seconds.

4.2.1. Test of Tensile Strength by Bending

• Three-Point Bending Test on prismatic specimens (4×4×16 cm³) with a loading rate of 50 N/s.

4.2.2. Compressive Strength Test

• Assessed using half-prisms from the flexural test, following NF EN 196-1 standards, using:

  • Compression stress calculation, typically based on the dimensions (4 x 4 cm cross-section) and load.

Task

• Given Data:

  • Flexural test load: 2000 N

  • Compressive test load: 45000 N

• Objective: Determine flexural and compressive strength at 28 days for the mentioned prism dimensions.

6. Uses of Mortars

6.2. Masonry Bonding

• Application: In construction with masonry units (blocks, bricks), mortars must ensure:

  • Sufficient mechanical properties for load transfer.

  • Adequate compactness for watertightness.

6.3. Coatings

• Mortar is one of the largest applications in coatings.

6.4. Screeds

• Function: Leveling slabs and providing surface regularity; can act as final finish or substrate for flooring.

6.5. Grouting and Bedding

• Industrial mortars tailored for specific applications, including:

  • Anchoring elements

  • Secondary structural works

  • Urban furniture placement (e.g., traffic signs).

5. Mortar Mix Design

• Importance of Proportions: Dosages of binder and sand impact mortar quality and strength.

• Precision: Critical to adhere to prescribed formulations to avoid strength compromise.

• Proportioning Methods:

  • By Volume: Typically involves ratios of 1:2-4 for sand and cement, e.g.:

  • Standard mortar: 1 cement, 3 sand, 1/2 water (S/C = 3, W/C = 0.5)

  • Fat lime mortar: 1 lime to 2 sand (S/C = 2)

  • Masonry mortar: 1 binder, 3 sand, 1/3 water (S/C = 3, W/C = 0.3)

  • By Weight: Reflects weight of binder in one cubic meter of finished mortar.

  • Common ratios (1:3 or 1:4 by volume) converted based on material densities for specific strength requirements.