Cheap fillers are added to concrete mixes to improve sustainability. Durability of such mixes is investigated. In this paper the sulfate resistance of mortar mixes containing crushed limestone and crushed dolomite fillers is investigated and compared to that of conventional mortar. Mortar mixtures with different ratios of dolomite or limestone of 10, 20, and 30%, introduced as partial cement replacement by weight, were tested to evaluate the effect of sulfate attack according to ASTM C 1012. Six prisms of each mix were exposed to sulfate for 10 weeks. It was concluded that the introduction of lime filler greatly reduces sulfate resistance while mixes containing dolomite fillers have almost the same sulfate resistance as conventional mixes.

PLC, portland limestone cement; PC, portland cement; PDC, portland dolomite cement; KCC, Kuwait cement company; KSS, Kuwaiti standards specifications; KBRC, Kuwaiti british ready mix company; NIC, national industries company of Kuwait; ASTMC, standard test method for compressive strength of hydraulic cement mortars

Portland cement is one of the most polluting materials with low sustainability as the cement industry is heavily energy consuming and it results in the release of a huge amount of carbon dioxide (CO2) which is one of the greenhouse gases. The world annual production of Portland cement is about 3 billion tons. The production of one ton of cement results in the release about 0.9 ton of CO2 into the environment. Greenhouse gases are the main cause of the currently experienced global warming. Due to its deleterious effects, it is necessary to reduce the CO2 release into environment. Several methods to reduce cement utilization have been investigated. One of those methods is the partial replacement of Portland cement with a ‘green’ material.¹

The utilization of some types of fillers is gaining popularity as a method to achieve a cheaper, more sustainable concrete, especially with high strength concrete with low water to cement ratio, where no enough water or space are available for full cement hydration. Limestone is the most common type of filler while Dolomite is another relatively new promising type of filler, locally available in Kuwait. Both types are considered in this study. The use of limestone fillers has been thoroughly investigated by many researchers. Portland Limestone cement (PLC) may be defined as cement that containing ground limestone as a partial replacement for Portland cement (PC). It is produced by blending Portland cement and limestone or intergrading Portland cement clinker, limestone, and calcium sulfate.² The performance of Portland limestone cement is almost similar to Portland cement. The ASTM and CSA specifications both limit the amount of limestone in Portland Limestone Cement to 15%. The purpose of using limestone is to reduce the amount of cement clinker, to reduce the consumption of raw materials, and to achieve sustainable concrete.^3,4

 Dolomite and limestone are considered carbonate rock. They are sedimentary rocks which can be grinded and used as a partial replacement for cement. Using dolomite as a partial replacement of cement to produce Portland Dolomite Cement (PDC) decreases the amount of cement which in turn reduces the CO2 emissions.⁵ Its use is not as common as limestone and research studies on the properties of dolomite as a partial cement replacement are limited.⁶

Deterioration and loss of durability is the main cause of premature loss of serviceability and termination of service life of buildings and structures in Kuwait. Sulfate attack is one of the common types of deterioration in Kuwait due the special characteristics of weather. The weather in Kuwait is characterized as hot marine environment. The very high temperature leads to much faster rate of deterioration. The investigation of sulfate resistance is, therefore, of great importance. The scope of these researches to investigate the sulfate resistance of mortars produced with 0, 10, 20 and 30% of crushed limestone and crushed dolomite introduced as partial replacement of cement by weight.

Portland cements Type I was provided by Kuwait cement company (KCC). This type of cement is produced in accordance with the Kuwaiti standards specifications (KSS 381-383), and the American specifications (ASTM C150). Coarse aggregate of Limestone with size (3/8 inches) was provided by Kuwaiti British Ready Mix Company (KBRC). The specific gravity of coarse lime stone used in this study was 2.37 % and the absorption was 0.3%. The limestone used was ground. Fine Ground dolomite was obtained from National Industries Company of Kuwait (NIC). The chemical composition ranges of the acquired type of dolomite are shown in Table 1. Particle size distributions of cement, limestone and dolomite are shown in Figure 1.

Figure 1 Particle Size Distribution for OPC, Limestone and Dolomite.

Fine Aggregates are natural sand, acquired from local quarries in Kuwait. Physical properties of fine aggregate are shown in Table 2. Constituent materials for mortars were proportioned according to ASTM C 1012 requirements such that the water to cement ratio was 0.485 and the sand to cement ratio was 2.75. Cement was partially replaced by crushed limestone and crushed dolomite at ratios of 0%, 10%, 20% and 30%, by weight, rendering seven different mortar mixes.⁷

Mixing and samples preparation

For each of the seven mixes, six mortar bars of sizes 25x25x280mm and three cubes of sizes 50x50x50mmwere cast. Mortar cubes were cast and tested according to ASTM C 109 (Standard Test Method for Compressive Strength of Hydraulic Cement Mortars). Mortars were mixed in small mixer, covered properly by plastic and placed in curing room at 35ºC. After 24 hours, specimens were remolded and stored in a water curing tank at 21±2ºC.

Testing and Properties

Mortar cubes were tested for compressive strength. The average compressive strengths for the seven mixes are shown in Table 3. Solution of Na₂SO₄ was prepared by dissolving 50 g of Na₂SO₄ in 1000 mL of distilled water; such that the volume proportions of the solution was 4 times the volume of mortar bars. Bars were then placed in the solution and kept at 21±2ºC as shown in Figure 2. Length change measurements were performed at 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 weeks after immersion in sulfate solution.

Figure 2 Mortar bars immersed in Na₂SO₄ solution.

According to ASTM C1012, when the maximum expansion of mortar bars exposed to sulfate solution for 6 months is less than 0.1%, then the cement can be considered as moderate sulfate resistance, while it can be classified as highly sulfate resistance when it reaches less than 0.05% after 6 months or reaches less than 0.1% after 12 months of exposure. Due to time restrictions, however, and as only a comparative study between conventional and filler mortars is required, samples were immersed for only 10 weeks. The variations of average expansions and time for the seven mortars are shown in Figures 3-5.

As shown in figures all samples experience expansion due to immersion in sulfate solution. The expansion increase with the immersion duration. The average expansion due to sulfate attack is much higher for mortars containing limestone than for conventional concrete. The average expansion for mortar prisms containing 10, 20 and 30% limestone as cement replacement after 10 weeks of immersion were 460, 520 and 630%, respectively, higher than that for conventional mortar. Results may be improved by increasing the limestone fineness. The fineness of the used limestone is higher than that of cement, and according to the fineness of limestone cement has to be 100-120 m2/Kg more than OPC to render similar properties. The type of limestone used in this study was selected due to its availability in the Kuwaiti market.

The sulfate resistance for mortars containing crushed dolomite filler is almost the same as that for conventional mortar. The average expansions for dolomite filler mortars are 150% and 40% higher than normal mortar for 20 and 30% dolomite, respectively, after 10 weeks of immersion. For 10% dolomite mortar, however, the expansion was 10% lower than that of conventional mortar. Sulfate resistance for dolomite filler mortars may also be improved by increasing crushed dolomite fineness.

In this paper, the sulfate resistance for mortars and concrete incorporating either crushed limestone or crushed dolomite filler as partial replacement of cement were investigated. The following were concluded:

1. The introduction of ground dolomite as a concrete filler resulted in concrete with analogues sulafte resistance to conventional concrete. The use of 10% dolomite as cement replacement increased resistance to sulafte attacks.
2. The utilization of crushed limestone filler as partial replacement of cement resulted in great reduction in concrete resistance to sulafte attacks. In case of sulafte presence other means to increase sulphate resistance such as using sulphate resistance concrete or pozzolanic materials should be considered.
3. Materials available in market were used in this investigation. Increasing the fineness of either dolomite or limestone is expected to improve sulphate resistance of concrete.
4. The use of fillers as partial cement replacement has great effect on concrete sustainability. Fillers reduce energy consumption in cement production and CO2 emission by the same ratio. Concrete sustainability also improves due to the increased service life resulting from increased durability.
5. Addition work is required to investigate the effect of the dolomite fineness on the properties and durability of resulting concrete.

The author declares no conflict of interest.

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